The Nasdaq Stock Market LLC v. SEC ( 2022 )


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  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued March 24, 2022                   Decided July 5, 2022
    No. 21-1167
    THE NASDAQ STOCK MARKET LLC, ET AL.,
    PETITIONERS
    v.
    SECURITIES AND EXCHANGE COMMISSION,
    RESPONDENT
    Consolidated with 21-1168, 21-1169
    On Petitions for Review of an Order
    of the Securities and Exchange Commission
    Thomas G. Hungar argued the cause for petitioners. With
    him on the briefs were Paul S. Mishkin, Amir C. Tayrani,
    Joshua M. Wesneski, Paul E. Greenwalt III, and Michael K.
    Molzberger. Matthew A. Kelley entered an appearance.
    Tracey A. Hardin, Assistant General Counsel, Securities
    and Exchange Commission, argued the cause for respondent.
    With her on the brief were Dan M. Berkovitz, General Counsel,
    Michael A. Conley, Solicitor, and Emily True Parise, Senior
    Litigation Counsel.
    2
    Robert A. Skinner and Douglas H. Hallward-Driemeier
    were on the brief for amicus curiae Investment Company
    Institute in support of respondent.
    Before: HENDERSON and WILKINS, Circuit Judges, and
    SENTELLE, Senior Circuit Judge.
    Opinion for the Court filed by Circuit Judge HENDERSON.
    KAREN LECRAFT HENDERSON, Circuit Judge: The
    Securities Exchange Act of 1934 (Exchange Act), 15 U.S.C.
    § 78a et seq., directs the Securities and Exchange Commission
    (Commission) to facilitate the establishment of a national
    market system (NMS), a key component of which is the public
    dissemination of market data regarding quotations for and
    transactions in equity securities. Equity market data is
    collected, consolidated and disseminated pursuant to NMS
    plans governed and operated by “self-regulatory
    organizations” (SROs), groups comprising, in large part, the
    major national securities exchanges for equity securities.
    Beginning in 2020, the Commission issued two orders aimed
    at consolidating the existing NMS plans governing the
    dissemination of equity market data into a single, consolidated
    plan (CT Plan) and modifying the governance structure to
    increase efficiencies, mitigate conflicts of interest among the
    securities exchanges and facilitate greater involvement by non-
    exchange stakeholders. See Order Directing the Exchanges and
    the Financial Industry Regulatory Authority To Submit a New
    National Market System Plan Regarding Consolidated Equity
    Market Data, 
    85 Fed. Reg. 28,702
     (May 13, 2020) (Governance
    Order); Order Approving, as Modified, a National Market
    System Plan Regarding Consolidated Equity Market Data, 
    86 Fed. Reg. 44,142
     (Aug. 11, 2021) (CT Plan Order).
    3
    A group of national securities exchanges associated with
    Nasdaq, Inc. (Nasdaq), the New York Stock Exchange (NYSE)
    and Cboe Global Markets (Cboe) (collectively, petitioners)
    challenge the Commission’s orders, arguing that several
    elements are arbitrary and capricious under the Administrative
    Procedure Act (APA), 
    5 U.S.C. § 551
     et seq., or contrary to the
    text and goals of the Exchange Act. In particular, petitioners
    challenge three provisions of the final, Commission-approved
    CT Plan: (1) the inclusion of representatives of non-SROs as
    voting members of the CT Plan’s operating committee; (2) the
    grouping of SROs based on corporate affiliation for voting; and
    (3) the requirement that the administrator of the CT Plan be
    “independent,” meaning independent of any SRO that sells
    equity market data products.
    As detailed infra, we grant petitioners’ three petitions as to
    the first challenged provision—non-SRO representation—and
    deny them in all other respects. Further, because the non-SRO-
    representation provision is not severable from the CT Plan
    Order, we vacate that Order in its entirety. We do, however,
    uphold in large part the Governance Order, which preceded the
    CT Plan Order and merely directed the SROs to propose an
    NMS plan that included the three challenged provisions.
    I. BACKGROUND
    A.
    In 1975, the Congress sought to modernize regulation of
    the securities markets through the establishment of a national
    market system to “distribute market data economically and
    equally and to promote fair competition among all market
    participants,” NetCoalition v. SEC, 
    615 F.3d 525
    , 528 (D.C.
    Cir. 2010), superseded by statute as stated in NetCoalition v.
    SEC, 
    715 F.3d 342
    , 344 (D.C. Cir. 2013); see also Bradford
    Nat’l Clearing Corp. v. SEC, 
    590 F.2d 1085
    , 1091 (D.C. Cir.
    4
    1978) (citing “operational breakdowns and economic
    distortions” in securities markets as impetus for reforms
    (quoting H.R. Rep. No. 94-229, at 91 (1975))), and its efforts
    culminated in the Securities Acts Amendments of 1975, Pub.
    L. No. 94-29, 
    89 Stat. 97
    . The Securities Acts Amendments
    granted the Commission “broad, discretionary powers” to
    ensure “maximum flexibility” in “oversee[ing] the
    development of a national market system” and
    “implement[ing] its specific components in accordance with
    the findings and . . . objectives” of the legislation. See S. Rep.
    94-75, at 7 (1975); see also Bradford, 
    590 F.2d at 1091
    .
    Of importance here, section 11A of the amended Exchange
    Act, Pub. L. No. 94-29, § 7, 
    89 Stat. 97
    , 111 (codified at 15
    U.S.C. § 78k-1), “direct[s]” the Commission to “facilitate the
    establishment of a national market system for securities . . . in
    accordance with the findings and to carry out the objectives set
    forth” in the section. 15 U.S.C. § 78k-1(a)(2). As to those
    statutory findings and objectives, the Congress concluded that
    “[i]t is in the public interest and appropriate for the protection
    of investors and the maintenance of fair and orderly markets to
    assure,” inter alia, “economically efficient execution of
    securities transactions,” “fair competition among” market
    participants and “the availability to brokers, dealers, and
    investors of information with respect to quotations for and
    transactions in securities.” Id. § 78k-1(a)(1)(C).
    To this end, section 11A “authorize[s]” the Commission,
    “by rule or order, to authorize or require self-regulatory
    organizations”—a group currently comprised in large part of
    the various securities exchanges, including petitioners—“to act
    jointly with respect to matters as to which they share authority
    under [the Exchange Act] in planning, developing, operating,
    or regulating a national market system (or a subsystem thereof)
    or one or more facilities thereof.” Id. § 78k-1(a)(3)(B); see also
    5
    id. § 78c(a)(26) (defining “self-regulatory organization”).
    Section 11A also creates a National Market Advisory Board—
    consisting of “persons associated with brokers and dealers
    (who shall be a majority) and persons not so associated who are
    representative of the public”—to advise the Commission on
    matters related to the national market system or its system of
    self-regulation by SROs. See id. § 78k-1(d). With respect to
    market data, section 11A authorizes the Commission to
    prescribe rules and regulations, “as necessary or appropriate”
    to carry out the Exchange Act’s purposes, to “assure the
    prompt, accurate, reliable, and fair collection, processing,
    distribution, and publication of information with respect to
    quotations for and transactions in . . . securities and the fairness
    and usefulness of the form and content of such information.”
    Id. § 78k-1(c)(1)(B).
    B.
    At “the heart of the national market system” is the
    collection, consolidation and dissemination of securities
    market data from the various securities exchanges. H.R. Rep.
    No. 94-229, at 93 (1975); see also NetCoalition, 
    615 F.3d at 529
    . In 2005, the Commission adopted Regulation NMS, 
    70 Fed. Reg. 37,496
     (June 29, 2005), in order to streamline and
    promote the availability of data regarding quotations for and
    transactions in securities. Before 2021, Regulation NMS
    required each securities exchange to report its “core” market
    data for its NMS-traded securities to one of two centralized
    securities information processors (SIPs), see 
    17 C.F.R. §§ 242.601
    , 242.602 (2020), which in turn consolidated and
    disseminated the core data to subscribers, including investors,
    broker-dealers and data vendors, see 
    id.
     § 242.603(a)–(b). See
    NetCoalition, 
    615 F.3d at 529
    . Consolidated core data for an
    NMS-traded security consisted of (1) the price, size and venue
    of the last sale; (2) each exchange’s current highest bid and
    6
    lowest offer; and (3) the highest bid and lowest offer currently
    available on any exchange. 
    Id.
     Possessing this data, “investors
    of all types have access to a reliable source of information for
    the best prices in NMS stocks.” Regulation NMS, 70 Fed. Reg.
    at 37,503.1
    At present, three SRO-administered NMS plans, known as
    the Equity Data Plans, govern the collection, consolidation and
    dissemination of core market data. Two plans, referred to by
    the Commission as the CTA and CQ Plans, cover Tape A, the
    consolidated data feed for securities listed on the NYSE, and
    Tape B, the data feed for securities listed on exchanges other
    than the NYSE and Nasdaq. The third plan, referred to as the
    UTP Plan, covers Tape C, the data feed for securities listed on
    Nasdaq. A NYSE affiliate serves as the SIP for Tapes A and B
    and Nasdaq is the SIP for Tape C. Subscribers to a particular
    data feed pay fees set according to the governing Equity Data
    Plan. Each Equity Data Plan is controlled by an operating
    committee, whose voting membership is limited to the SROs
    participating in the particular plan. Each plan also has an
    1
    Parallel to the Commission orders at issue here, the
    Commission proposed and approved a rule amending Regulation
    NMS’s “centralized consolidation model” for securities market data
    by expanding the definition of core market data and facilitating
    greater competition among data consolidators. See generally Market
    Data Infrastructure, 
    86 Fed. Reg. 18,596
     (Apr. 9, 2021). We recently
    upheld the rule against challenges from these petitioners. See
    generally Nasdaq Stock Mkt. LLC v. SEC, 
    34 F.4th 1105
     (2022).
    Although tangentially related to the petitions at issue here, the
    Market Data Infrastructure rule is not pertinent to their resolution;
    the Commission itself has iterated that with respect to the Market
    Data Infrastructure rule and the orders at issue here, “[n]either
    initiative depends on the other initiative being implemented before it
    may take effect.” Order Denying Stay, Exchange Act Release No.
    93,051, at 6 (Sept. 17, 2021), 
    2021 WL 4267323
    , at *7 (alteration in
    original and citation omitted).
    7
    administrator which, among other things, supervises the audit
    process for data subscriber usage and fee payments. The NYSE
    serves as administrator for the CTA and CQ Plans and Nasdaq
    serves as administrator for the UTP Plan.
    C.
    Since the adoption of Regulation NMS, the Commission
    has observed two notable changes regarding the structure of the
    equity markets. First, although securities exchanges were once
    nonprofit entities mutually owned by their members—meaning
    those companies whose stock is traded on the exchange—they
    are now, generally speaking, demutualized and for-profit
    entities owned by shareholders that sell proprietary-data
    products. These proprietary-data products often contain
    exchange-specific data that goes beyond the best bid and best
    offer quotes contained in the core data feeds and are generally
    delivered much faster than the core data feeds, thereby
    resulting in what the Commission characterizes as a “two-
    tiered market-data environment.” Notice of Proposed Order
    Directing the Exchanges and the Financial Industry Regulatory
    Authority to Submit a New National Market System Plan
    Regarding Consolidated Equity Market Data, 
    85 Fed. Reg. 2,164
    , 2,169 (Jan. 14, 2020) (Proposed Governance Order).
    Second, the emergence of “exchange groups”—multiple
    exchanges operating under the same corporate umbrella—has
    “consolidat[ed] much of the voting power and control of the
    Equity Data Plans” and resulted in uniform voting by blocs of
    four or five votes. 
    Id. at 2,168
    . The Commission also observed
    that these exchange groups—which could command a majority
    of votes on the Equity Data Plans’ operating committees—are
    the “primary producers of exchange proprietary data products.”
    
    Id. at 2,175
    . The Commission concluded that the confluence of
    these two developments has created and exacerbated conflicts
    of interests between exchanges’ business interests and
    8
    regulatory obligations under the Exchange Act, 
    id.,
     and
    “perpetuates disincentives for the Equity Data Plans to invest
    in certain improvements to enhance the distribution of core
    data or the content of the core data itself,” 
    id. at 2,170
    .
    In response to these perceived deficiencies in the Equity
    Data Plans, the Commission issued its Proposed Governance
    Order, which proposed to direct the SROs to formulate and
    propose a single “New Consolidated Data Plan” (later renamed
    the CT Plan) to replace the three Equity Data Plans. See
    generally Proposed Governance Order, 
    85 Fed. Reg. 2,164
    .
    Despite largely leaving the formulation of the CT Plan up to
    the SROs, the Commission set out three governance features.
    First, the CT Plan’s operating committee would include
    representatives of six classes of equity market participants:
    institutional investors, broker-dealers with a predominantly
    retail investor customer base, broker-dealers with a
    predominantly institutional investor customer base, securities
    market-data vendors, issuers of NMS stock and retail investors.
    
    Id. at 2,179
    . These representatives would serve as voting
    members on the operating committee administering the CT
    Plan, collectively controlling one-third of the committee’s
    voting power—using fractional votes to preserve the ratio. 
    Id. at 2
    ,180–81.
    Second, the Commission recommended allocating the
    votes held by the SROs according to an SRO’s corporate
    affiliation. Each “exchange group” (later called SRO Groups),
    defined as “multiple exchanges operating under one corporate
    umbrella,” 
    id. at 2,168
    , and “unaffiliated SRO,” meaning an
    SRO not affiliated with another SRO, 
    id. at 2
    ,175 n.140, would
    be granted one vote on the operating committee, 
    id. at 2,175
    .
    Each exchange group or unaffiliated SRO would have an
    additional vote if it has a “consolidated equity market share”
    9
    greater than 15%.2 
    Id. at 2
    ,175–76. As an illustration, the SROs
    under the NYSE’s umbrella—New York Stock Exchange
    LLC, NYSE American LLC, NYSE Arca, Inc., NYSE
    Chicago, Inc., and NYSE National, Inc.—would be treated as
    one SRO Group and receive two votes, instead of receiving one
    vote for each SRO. Relatedly, the existing unanimity
    requirement for certain operating-committee actions would be
    replaced by an “augmented majority vote”—defined by the
    Commission as a “two-thirds majority of all votes on the
    operating committee, provided this vote also includes a
    majority of the SRO votes,” meaning SRO Group votes. 
    Id. at 2,181
    .
    Third, the Commission proposed requiring that the CT
    Plan administrator be “independent,” meaning “not . . . owned
    or controlled by a corporate entity that separately offers for
    sale” its own proprietary-data products. 
    Id. at 2,183
    . The
    independence requirement would preclude both of the current
    Equity Data Plan administrators—the NYSE and Nasdaq—
    from subsequently serving as the CT Plan administrator.
    After notice and comment, the Proposed Governance
    Order was finalized and approved without material change. See
    Governance Order, 
    85 Fed. Reg. 28,702
    . The SROs complied
    with the Governance Order, submitting a proposed CT Plan
    that included the three features proposed by the Commission,
    2
    The 15% threshold was selected in order to “limit[] the total
    votes available to an exchange group or unaffiliated exchange to two
    votes.” Proposed Governance Order, 85 Fed. Reg. at 2,176. The
    Commission concluded that the consolidated market shares of the
    largest exchange groups range from 17% to 23% and that setting the
    threshold for an additional vote at 10% would “suggest that a third
    vote would be appropriate at 20% of consolidated equity market
    share,” thereby giving some exchange groups a third vote
    unavailable to the unaffiliated exchanges. Id.
    10
    see Notice of Filing of a National Market System Plan
    Regarding Consolidated Equity Market Data, 
    85 Fed. Reg. 64,565
     (October 13, 2020), while at the same time reserving
    their objections to the legality of the three features, see Joint
    Appendix 209 n.13 (NYSE Comment Letter). Petitioners
    sought review of the Governance Order but we dismissed the
    challenge, concluding that the Commission had not committed
    to any particular governance structure and therefore the
    Governance Order did not constitute reviewable final agency
    action. See Nasdaq Stock Mkt. LLC v. SEC, 
    1 F.4th 34
    , 37–38,
    39 (D.C. Cir. 2021); see also 15 U.S.C. § 78y(a)(1).
    In August 2020, the Commission approved the proposed
    CT Plan. See CT Plan Order, 
    86 Fed. Reg. 44,142
    . Petitioners
    timely filed for review, challenging the three Commission-
    recommended features. Petitioners also filed with the
    Commission a motion to stay the CT Plan Order, which the
    Commission denied. Petitioners then filed for and received a
    stay from this Court. See Order, Nasdaq Stock Mkt. LLC v.
    SEC, No. 21-1167 (D.C. Cir. Oct. 13, 2021). We have
    jurisdiction of their challenge pursuant to section 25(a) of the
    Exchange Act. See 15 U.S.C. 78y(a)(1).
    II. ANALYSIS
    Petitioners’ challenge reaches both the Commission’s
    interpretation of section 11A of the Exchange Act as well as its
    decisionmaking given the record and comments before it. As
    to the former, we review using the familiar Chevron two-step
    framework. See Chevron, U.S.A., Inc. v. Nat. Res. Def. Council,
    Inc., 
    467 U.S. 837
    , 842–43 (1984). At step one, we ask
    “whether the agency-administered statute is ambiguous on the
    precise question at issue.” Eagle Pharms., Inc. v. Azar, 
    952 F.3d 323
    , 330 (D.C. Cir. 2020) (internal quotation marks
    omitted) (quoting Guedes v. Bureau of Alcohol, Tobacco,
    11
    Firearms & Explosives, 
    920 F.3d 1
    , 28 (D.C. Cir. 2019)). If
    not, we assume at step two that the “Congress has empowered
    the agency to resolve the ambiguity” and accordingly defer to
    the agency’s interpretation so long as it is a reasonable
    construction of the statute. Util. Air Reg. Grp. v. EPA, 
    573 U.S. 302
    , 315 (2014).
    In addition, we may set aside a Commission order if it is
    found to be “arbitrary, capricious, an abuse of discretion, or
    otherwise not in accordance with law.” 
    5 U.S.C. § 706
    (2)(A);
    see NetCoalition, 
    615 F.3d at 532
    . Besides adhering to
    statutory and regulatory requirements, the Commission is
    required to “examine the relevant data and articulate a
    satisfactory explanation for its action including a ‘rational
    connection between the facts found and the choice made.’”
    Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto
    Ins. Co., 
    463 U.S. 29
    , 43 (1983) (quoting Burlington Truck
    Lines v. United States, 
    371 U.S. 156
    , 168 (1962)). The
    Commission’s factual findings are conclusive if supported by
    substantial evidence. See 15 U.S.C. § 78y(a)(4); NetCoalition,
    
    615 F.3d at 533
    .
    Petitioners challenge the Commission’s CT Plan Order
    and Governance Order on three grounds: First, the Commission
    exceeded its authority under both section 11A of the Exchange
    Act and Rule 608 of Regulation NMS by placing
    representatives of non-SROs on the CT Plan’s operating
    committee as voting members. Second, the Commission’s
    decision to group SROs based on corporate affiliation for
    voting purposes is contrary to law, as it prevents SROs from
    “act[ing] jointly” to effectuate the CT Plan, and it is otherwise
    arbitrary and capricious by failing to explain adequately the
    Commission’s departure from its past practice of treating
    affiliated and unaffiliated SROs the same. Third, the
    Commission’s requirement that the administrator of the CT
    12
    Plan be “independent”—not owned or controlled by a
    corporate entity that directly or indirectly sells proprietary-data
    products that compete with the core data feed—is arbitrary and
    capricious. We ultimately agree with petitioners as to their first
    challenge but reject their second and third challenges.
    A. Non-SRO Membership on CT Plan Operating
    Committee
    To begin, the Commission does not argue that its
    interpretation of section 11A of the Exchange Act as permitting
    non-SRO representation on the CT Plan operating committee
    is necessarily compelled by the statute; the Commission instead
    argues that the “Congress has not ‘directly spoken to th[is]
    precise’ issue.” See Resp’t Br. 29 n.3 (alteration in original)
    (quoting City of Clarksville v. FERC, 
    888 F.3d 477
    , 482 (D.C.
    Cir. 2018)); see also Oral Arg. Tr. 19:25–20:1 (Commission is
    “not arguing that the statute is clear at Chevron [step one]”); 
    id.
    at 20:15–18 (“[I]n the [1975] [A]mendments, Congress very
    specifically did not make a decision as to the precise manner in
    which the national market system was going to be structured.”).
    Our ordinary course of action would be to first determine
    whether section 11A is, as the Commission suggests, silent or
    ambiguous as to non-SRO representation issue; if so, we would
    then assess whether the Commission’s permissive
    interpretation, as embodied in the various orders at issue, is
    reasonable. See Chevron, 
    467 U.S. at
    842–43. Occasionally,
    however, we have assumed arguendo that a statute is
    ambiguous or silent and proceeded to the second step of the
    Chevron analysis. See, e.g., Good Fortune Shipping SA v.
    Comm’r, 
    897 F.3d 256
    , 261 (D.C. Cir. 2018); Lubow v. U.S.
    Dep’t of State, 
    783 F.3d 877
    , 884 (D.C. Cir. 2015); U.S. Postal
    Serv. v. Postal Regul. Comm’n, 
    599 F.3d 705
    , 710 (D.C. Cir.
    2010); see also Babbitt v. Sweet Home Chapter of Cmtys. for a
    13
    Great Or., 
    515 U.S. 687
    , 703 (1995). We do so here, confident
    in doing so because the Commission has failed to demonstrate
    that its construction of section 11A is reasonable.3
    At Chevron step two, we ask whether the agency’s
    interpretation is “arbitrary or capricious in substance, or
    manifestly contrary to the statute.” Good Fortune Shipping,
    897 F.3d at 261 (quoting Mayo Found. for Med. Educ. &
    Research v. United States, 
    562 U.S. 44
    , 53 (2011)); see also
    Village of Barrington v. Surface Transp. Bd., 
    636 F.3d 650
    , 665
    (D.C. Cir. 2011) (asking “whether the [agency] has reasonably
    explained how the permissible interpretation it chose is
    ‘rationally related to the goals of’ the statute” (quoting AT&T
    Corp. v. Iowa Utils. Bd., 
    525 U.S. 366
    , 388 (1999))).
    Importantly, “[t]he reasonableness of an agency’s construction
    depends on the construction’s fit with the statutory language as
    well as its conformity to statutory purposes.” Abbott Labs. v.
    Young, 
    920 F.2d 984
    , 988 (D.C. Cir. 1990) (internal quotation
    marks omitted); see also Van Hollen v. FEC, 
    811 F.3d 486
    , 492
    (D.C. Cir. 2016) (“The starting place for any Chevron Step
    Two inquiry is the text of the statute.”).
    Begin with the primary textual hook for the Commission’s
    decision: section 11A(a)(3)(B) states that “[t]he Commission is
    authorized . . . to authorize or require self-regulatory
    organizations to act jointly with respect to matters as to which
    they share authority under [the Exchange Act] in planning,
    developing, operating, or regulating a national market system
    (or a subsystem thereof) or one or more facilities thereof.” 15
    U.S.C. § 78k-1(a)(3)(B); see also CT Plan Order, 86 Fed. Reg.
    at 44,157 (“Here, the Commission is acting pursuant to its
    3
    Because we find the Commission’s interpretation of section
    11A—the principal basis for its asserted statutory authority—
    unreasonable at Chevron step two, we do not address petitioners’
    parallel argument regarding Rule 608 of Regulation NMS.
    14
    authority under Section 11A(a)(3)(B) . . . .”). The Congress
    explicitly reserved a role for SROs in developing and
    effectuating NMS plans, at the Commission’s discretion. The
    statute is silent, however, with respect to many details of
    whatever joint action the Commission so authorizes.
    The Commission contends that the statutory silence allows
    it the discretion to direct SROs to formulate an NMS plan that
    permits non-SRO involvement in NMS planning and
    governance, albeit in a minority voting role. See Resp’t Br. 25–
    26. But section 11A(a)(3)(B) specifically identifies SROs that
    “share authority under [the Exchange Act]” as those the
    Commission authorizes to “act jointly . . . in planning,
    developing, operating, or regulating a national market system,”
    15 U.S.C. § 78k-1(a)(3)(B), making it less likely that there is a
    “gap[]” for the Commission to fill with respect to what entities
    may act jointly, see Ethly Corp. v. EPA, 
    51 F.3d 1053
    , 1060
    (D.C. Cir. 1995). This is the maxim of expressio unius est
    exclusio alterius at work: “[M]ention of one thing”—SROs—
    “implies exclusion of another thing”—non-SROs. Ethyl Corp,
    
    51 F.3d at 1061
     (quoting Am. Methyl Corp. v. EPA, 
    749 F.2d 826
    , 835–36 (D.C. Cir. 1984)). Application of the canon here
    is analogous to its application in Halverson v. Slater, 
    129 F.3d 180
     (D.C. Cir. 1997), where we applied the expressio unius
    canon in interpreting 
    46 U.S.C. § 2104
    (a), which provides that
    the Secretary of Transportation may delegate certain duties “to
    any officer, employee, or member of the Coast Guard,” to
    preclude delegation to non-Coast Guard officials. Halverson,
    
    129 F.3d at
    184–86. We did so notwithstanding the Secretary’s
    general statutory authority to delegate to subordinates, see 
    49 U.S.C. § 322
    , finding that “the more specific provision
    controls.” Halverson, 
    129 F.3d at 186
    . Thus, although the
    Commission is correct that the Congress did not insert the word
    “exclusively” into section 11A(a)(3)(B), see Resp’t Br. 28–29,
    15
    the language it did choose evinces exclusivity that, in our
    reading, forecloses the Commission’s desired interpretation.
    Granted, the weight of the expressio unius canon is
    sensitive to statutory context, especially in the administrative
    realm where the “Congress is presumed to have left to
    reasonable agency discretion questions that it has not directly
    resolved.” Adirondack Med. Ctr. v. Sebelius, 
    740 F.3d 692
    , 697
    (D.C. Cir. 2014) (quoting Cheney R.R. Co. v. I.C.C., 
    902 F.2d 66
    , 68–69 (D.C. Cir. 1990)); see also Indep. Ins. Agents of Am.,
    Inc. v. Hawke, 
    211 F.3d 638
    , 644 (D.C. Cir. 2000). But “where
    the context shows that the ‘draftsmen’s mention of one thing,
    like a grant of authority, does really necessarily, or at least
    reasonably, imply the preclusion of alternatives,’ the canon is
    a useful aide.” Hawke, 
    211 F.3d at 644
     (quoting Shook v. D.C.
    Fin. Resp. & Mgmt. Assistance Auth., 
    132 F.3d 775
    , 782 (D.C.
    Cir. 1998)).
    Here, several aspects of the statutory context cut against
    the Commission’s interpretation. First, the Commission’s
    reading of section 11A(a)(3)(B) both to expressly identify
    SROs as those entities that can act jointly in developing and
    effectuating the national market system and to authorize by
    implication a non-SRO to exercise similar governance
    authority would render the former superfluous. See TRW Inc.
    v. Andrews, 
    534 U.S. 19
    , 31 (2001) (“[A] statute ought, upon
    the whole, to be so construed that, if it can be prevented, no
    clause, sentence, or word shall be superfluous, void, or
    insignificant.” (quoting Duncan v. Walker, 
    533 U.S. 167
    , 174
    (2001)). Further, we have observed that the canon against
    surplusage and the expressio unius canon “are at their zenith
    when they apply in tandem,” as they appear to do here. Hawke,
    
    211 F.3d at 645
    . The Commission’s only counter is that the
    express mention of SROs as those entities that may act jointly
    was to alleviate antitrust concerns. See Resp’t Br. 36–38. But
    16
    the antitrust explanation, even if assumed to be plausible and
    supported by the legislative history, fails to answer the key
    question whether section 11A(a)(3)(B) implicitly permits non-
    SROs in governance.
    Second, section 11A(a)(3)(B) specifies that SROs may be
    authorized “to act jointly with respect to matters as to which
    they share authority under [the Exchange Act] in planning,
    developing, operating, or regulating a national market system.”
    15 U.S.C. § 78k-1(a)(3)(B) (emphasis added). Such shared
    authority includes, inter alia, the specified duties “to protect
    investors and the public interest,” id. § 78f(b)(5); see also id.
    §§ 78o-3(b)(6), 78q-1(b)(3)(F), the promulgation of internal
    rules subject to Commission approval, see id. § 78s(b), and the
    obligations to “comply” and “enforce compliance” with the
    provisions of the Exchange Act, rules and regulations
    thereunder and its own rules, id. § 78s(g)(1). The “share
    authority” language thus qualifies the SROs’ quasi-regulatory
    authority and also explains why SROs are granted such
    authority. The non-SROs and their representatives, on the other
    hand, lack similarly unifying statutory and regulatory
    obligations and the Commission has acknowledged as much.
    See CT Plan Order, 86 Fed. Reg. at 44,154 (“Non-SRO Voting
    Representatives will not have the same legal obligations as the
    SRO Voting Representatives . . . .”); id. at 44,168 (“Non-SRO
    Voting Representatives will serve on the Operating Committee
    in their individual capacity and do not have regulatory
    obligations paralleling those of the SROs . . . .”). The
    Commission has not adequately explained why the Congress
    expressly highlighted the SROs’ shared authority under the
    Exchange Act as support for their authority pursuant to section
    11A and at the same time impliedly gave similar section 11A
    authority to entities that lack such shared authority under the
    Exchange Act.
    17
    Third, and finally, elsewhere in section 11A, the
    Commission is authorized to create advisory committees and
    employ outside experts, see 15 U.S.C. § 78k-1(a)(3)(A), as
    well as establish a “National Market Advisory Board”
    consisting of “persons associated with brokers and dealers” and
    certain “representative[s] of the public,” id. § 78k-1(d)(1).
    Thus, it cannot be said that the Congress was agnostic about
    the role of non-SROs in the national market system. Instead, it
    appears to us that the Congress “considered the unnamed
    possibility” of non-SROs serving in a regulatory or quasi-
    regulatory role in the national market system “and meant to say
    no to it” by providing a separate, advisory role for them. Marx
    v. Gen. Revenue Corp., 
    568 U.S. 371
    , 381 (2013) (quoting
    Barnhart v. Peabody Coal Co., 
    537 U.S. 149
    , 168 (2003).
    In addition to section 11A(a)(3)(B), the Commission
    invokes section 11A(c)(1)(B), see CT Plan Order, 86 Fed. Reg.
    at 44,142 & n.14, 44,157; see also Resp’t Br. 25–26, 29, 31,
    which provides, in relevant part:
    No self-regulatory organization, member
    thereof, securities information processor,
    broker, or dealer shall . . . collect, process,
    distribute, publish, or prepare for distribution or
    publication any information with respect to
    quotations for or transactions in any security . . .
    in contravention of such rules and regulations as
    the Commission shall prescribe as necessary or
    appropriate in the public interest, for the
    protection of investors, or otherwise in
    furtherance of the purposes of this chapter to . . .
    assure the prompt, accurate, reliable, and fair
    collection, processing, distribution, and
    publication of information with respect to
    quotations for and transactions in such
    18
    securities and the fairness and usefulness of the
    form and content of such information[.]
    15 U.S.C. § 78k-1(c)(1)(B). In the Commission’s view, this
    provision supports its overarching interpretation that section
    11A “necessarily contemplates the involvement of non-SROs
    in the collection, processing, distribution and publication of
    market data, because it prohibits them from doing any of those
    things in contravention of rules prescribed by the
    Commission.” Resp’t Br. 29; see also CT Plan Order, 86 Fed.
    Reg. at 44,157 & n.241.
    But section 11A(c)(1)(B), which says nothing about the
    national market system or its development or operation, merely
    indicates that non-SROs, specifically SIPs and broker-dealers,
    play enough of a role in the dissemination of market data to
    warrant granting the Commission antifraud authority to police
    non-SROs. Cf. 15 U.S.C. § 78j (antifraud provision using
    similar language). It does little to support the Commission’s
    interpretation that those same non-SROs are meant to play an
    affirmative role in the planning and operation of an NMS plan.
    Further, even if section 11A(c)(1)(B) could be read the way the
    Commission asserts, its general grant of authority does not
    override the more narrowly tailored section 11A(a)(3)(B). See,
    e.g., Gozlon-Peretz v. United States, 
    498 U.S. 395
    , 407 (1991)
    (“A specific provision controls over one of more general
    application.”).
    In short, even assuming the Commission is correct that
    section 11A is ambiguous or silent on the issue of non-SRO
    representation in NMS plan governance, it nevertheless fails to
    anchor its interpretation to any reasonable reading of section
    11A. As a result, the Commission’s decision to include
    representatives of non-SROs on the CT Plan operating
    19
    committee is unreasonable and therefore invalid under
    Chevron step two.
    B. SRO Groups
    Petitioners next object to the Commission’s decision to
    allocate and limit SRO votes according to an SRO’s corporate
    affiliation with another SRO, arguing that the decision is
    contrary to section 11A and otherwise arbitrary and capricious.
    As explained below, we find petitioners’ arguments on this
    issue are without merit.
    1. “Contrary to Law”
    To begin, petitioners make two arguments that center on
    the text of section 11A of the Exchange Act. First, they point
    to the statutory definition of “self-regulatory organization,”
    which includes “any national securities exchange.” 15 U.S.C.
    § 78c(a)(26). Petitioners construe this definition to mean “any
    and all exchanges . . . each of which is a discrete, legally
    distinct entity” and argue that SRO Groups prevent an
    individual SRO from being recognized as an SRO for the
    purpose of joint action under section 11A(a)(3)(B). Pet’rs
    Reply Br. 21 (emphasis in original). Second, petitioners
    contend that the combination of SRO Groups and the
    augmented majority voting structure—which requires a
    majority of SRO votes and a two-thirds majority of all votes,
    including non-SROs—would permit committee approval even
    if there is opposition from a majority of individual SROs. See
    Pet’rs Br. 43–46. As an example,
    a proposal that is supported by all of the non-
    SRO voting representatives (a total of four-and-
    a-half votes), the four unaffiliated SROs, and
    the Nasdaq-affiliated SRO Group (with two
    votes for its three exchanges) would have
    20
    sufficient support to be adopted under the
    Commission’s voting framework. But assuming
    that the nine remaining SROs opposed the
    proposal, the proposal would be supported by
    only seven out of the sixteen individual SROs.
    Id. at 45. As petitioners see it, this outcome “erects a barrier to
    ‘joint[]’ SRO operation of the CT Plan that is incompatible
    with the Exchange Act.” Id. at 46 (quoting 15 U.S.C.§ 78k-
    1(a)(3)(B)).
    Because we find that the Commission failed to provide a
    reasonable interpretation of section 11A that would permit non-
    SRO representation in the first place, see supra p. 12–19, we
    see little need to address hypothetical voting outcomes among
    the SRO Groups and non-SROs or whether a particular
    outcome would “erect[] a barrier” to joint action pursuant to
    section 11A, as petitioners contend.
    The crux of petitioners’ remaining arguments is that
    section 11A(a)(3)(B) requires that each SRO, as defined in the
    Exchange Act, be on equal terms with respect to the
    governance of NMS plans, including voting. Yet nothing in
    section 11A appears to require the strict one-to-one voting
    representation by individual SROs contemplated by
    petitioners. For one thing, although petitioners are correct that
    the term “self-regulatory organization” is defined at the
    individual level in the definitions section of the statute, the use
    of its plural form in section 11A(a)(3)(B) simply establishes the
    universe of entities (i.e., SROs) that may be authorized by the
    Commission to act jointly—and no party argues that the
    Commission excludes any SROs from the CT Plan operating
    committee. Thus, the definition of “self-regulatory
    organization” sheds little, if any, light as to how the
    21
    Commission may allocate NMS plan operating committee
    votes among individual SROs.
    Moreover, the undefined term “act jointly,” given its
    ordinary meaning, see Sorenson Commc’ns, LLC v. FCC, 
    897 F.3d 214
    , 228 (D.C. Cir. 2018) (attributing to undefined
    statutory term “its ordinary meaning”), simply means to act
    cooperatively, together or in conjunction, see, e.g., Jointly, The
    Oxford English Dictionary (2d ed. 1989) (“[t]ogether, in
    union” and “[i]n conjunction, combination, or concert”);
    Jointly, Webster’s Third New International Dictionary (1981)
    (“together” and “unitedly”); Jointly, Ballentine’s Law
    Dictionary (3d ed. 1969) (“[u]nitedly” and “sharing together”).
    “Jointly” does not require a particular level of involvement
    among the individual members—such as “one SRO, one vote,”
    as petitioners seem to suggest—so long as all participants are
    involved to some degree. Section 11A(a)(3)(B) does not
    specify many details as to how the Commission may set the
    contours of SRO joint action. The provision makes no mention
    of NMS plans, operating committees or administrators yet no
    party objects to the Commission’s use of those governance
    structures. This, in our view, makes it unlikely that the
    Congress would combine broad Commission discretion to fill
    in the details of whatever governance structure it envisions
    with an unusually rigid understanding of “act jointly” that
    requires one-to-one representation. Thus, we see little merit to
    petitioners’ textual arguments.
    2. Departure from Commission Precedent and Disparate
    Treatment
    Aside from the text of section 11A, petitioners contend
    that the Commission’s use of SRO Groups departs from the
    Commission’s past practice of treating affiliated SROs as
    distinct legal entities in other regulatory settings and subjects
    22
    affiliated SROs to less favorable treatment as compared to
    unaffiliated SROs. Again, we find these arguments without
    merit.
    Petitioners first cite several matters in which the
    Commission has required individual SROs to maintain their
    separate regulatory identity. See, e.g., Order Setting Aside
    Action by Delegated Authority and Approving Proposed Rule
    Change Relating to NYSE Arca Data, 
    73 Fed. Reg. 74,770
    ,
    74,790 (Dec. 9, 2008) (separate pools of liquidity); Order
    Disapproving Proposed Rule Change to Offer a Rebate Based
    on Members’ Aggregate Customer Volume in Multiply-Listed
    Options Transacted on NASDAQ OMX PHLX LLC or Its
    Affiliated Options Exchanges, 
    79 Fed. Reg. 42,578
    , 42,585–86
    (July 22, 2014) (separate rebate schedules). But the fact that the
    Commission treats SROs as distinct and separate entities vis-à-
    vis their individual statutory and regulatory obligations does
    not necessarily mandate similar treatment of NMS plans where
    SROs act collectively to effectuate a market-wide plan. The
    Commission made this precise point. See CT Plan Order, 86
    Fed. Reg. at 44,164 (“But both the applicable legal
    requirements and the function being performed here by the
    SROs differ in the context of the responsibility of the SROs to
    jointly operate the NMS plans pursuant to Section 11A of the
    Act and to disseminate consolidated market data, to which
    different SROs may contribute in varying degrees.”).
    Petitioners next point to the Commission’s past practice of
    treating SROs individually with respect to earlier NMS plan
    operating committees. See, e.g., Order Approving the National
    Market System Plan Governing the Consolidated Audit Trail,
    
    81 Fed. Reg. 84,696
    , 84,948 (Nov. 23, 2016). We have often
    recognized that an agency must acknowledge and explain its
    departure from past policy. See Sw. Airlines Co. v. FERC, 
    926 F.3d 851
    , 856 (D.C. Cir. 2019). “A central principle of
    23
    administrative law is that, when an agency decides to depart
    from decades-long past practices and official policies, the
    agency must at a minimum acknowledge the change and offer
    a reasoned explanation for it.” Am. Wild Horse Pres. Campaign
    v. Perdue, 
    873 F.3d 914
    , 923 (D.C. Cir. 2017) (citing Encino
    Motorcars, LLC v. Navarro, 
    579 U.S. 211
    , 221–22 (2016)).
    Here, the Commission easily cleared the “not . . .
    especially high bar” of acknowledging and explaining its
    departure. Sw. Airlines, 926 F.3d at 856. It acknowledged
    comments about the differing treatment of SROs for voting,
    recognized that “the Commission’s treatment of corporate
    affiliations varies based on the particular facts and
    circumstances” and took into account corporate affiliation for
    voting “[b]ecause of the concentrated power affiliated SROs
    exert in the governance structure of consolidated equity market
    data, as demonstrated by the indisputable fact that affiliated
    SROs vote as blocs.” CT Plan Order, 86 Fed. Reg. at 44,164.
    The Commission iterated its findings that “[i]ndividual
    exchanges that historically had only one vote on NMS plans
    are now a part of groups that can control blocs of four or five
    votes,” id., and that “‘in its oversight of the Equity Data Plans,
    [it] is unaware of an individual affiliated exchange member’
    ever having ‘cast its vote differently than the votes cast by its
    affiliated exchanges,’” id. (quoting Governance Order, 85 Fed.
    Reg. at 28,713), in support of its decision to use group-based
    voting. The Commission also stated its “belie[f] that
    reallocating votes by SRO Group should help to ensure the
    prompt, accurate, reliable, and fair collection, processing,
    distribution, and publication of” NMS market data. Id.
    As their final argument, petitioners object to the
    Commission’s decision on the ground that it subjects affiliated
    SROs to less favorable treatment than unaffiliated SROs,
    without adequate explanation. As a general principle, agency
    24
    action “is at its most arbitrary when it treats similarly situated
    people differently,” Etelson v. Off. of Pers. Mgmt., 
    684 F.2d 918
    , 926 (D.C. Cir. 1982), meaning that agencies must
    “provide an adequate explanation to justify treating similarly
    situated parties differently,” Burlington N. and Santa Fe Ry.
    Co. v. Surface Transp. Bd., 
    403 F.3d 771
    , 776 (D.C. Cir. 2005).
    But here, the Commission has provided an adequate
    explanation, citing the need to mitigate the Equity Data Plans’
    practical dilution of unaffiliated exchanges’ voting power. In
    response to comments that the SRO-Group-based voting
    system would unfairly dilute the votes of affiliated exchanges,
    the Commission countered that any perceived disparate
    treatment between affiliated and unaffiliated exchanges was
    justified “from a policy perspective because of the
    disproportionate influence affiliated exchange groups currently
    exercise in [Equity Data] Plan matters by voting as a block and
    diluting the voting power of other Participants.” Governance
    Order, 85 Fed. Reg. at 28,713. The Commission also reasoned
    that “bloc voting has diluted the voting power of unaffiliated
    SROs over time, and that this concentration of ‘voting power
    in a small number of exchange group stakeholders, which also
    have inherent conflicts of interest,’ has ‘perpetuated
    disincentives for the Equity Data Plans to make improvements
    to the SIP data products.’” CT Plan Order, 86 Fed. Reg. at
    44,164 (quoting Governance Order, 85 Fed. Reg. at 28,713).
    C. Independent Administrator
    Petitioners’ final objection is to the Commission’s
    decision that the CT Plan administrator must be
    “independent”—meaning “not . . . owned or controlled by a
    corporate entity that, either directly or via another subsidiary,
    offers for sale its own [proprietary-data products].” CT Plan
    Order, 86 Fed. Reg. at 44,195. The Commission supported the
    independence requirement by noting that “an entity that acts as
    25
    the administrator while also offering for sale its own
    proprietary data products faces a substantial, inherent conflict
    of interest, because it would have access to sensitive SIP
    customer information of significant commercial value.” Id.; see
    also id. at 44,196 (“Unlike the exchanges that offer for sale
    their own proprietary equity market data products, an
    independent Administrator would not have the competing
    objective of maximizing its own proprietary data products’
    profitability.”). Petitioners make three arguments in support of
    their contention that the Commission failed to articulate a
    rational explanation for its decision, none of which we find
    persuasive.
    Petitioners first contend that the Commission failed to
    substantiate its “purely theoretical” concern that a CT Plan
    administrator could misappropriate confidential information,
    such as by pointing to a plan administrator’s past misconduct
    or by highlighting the shortcomings of existing safeguards.
    Pet’rs Br. 54. Granted, an agency is generally on sounder
    footing when it “act[s] upon the basis of empirical data.”
    Chamber of Com. of U.S. v. SEC, 
    412 F.3d 133
    , 142 (D.C. Cir.
    2005). But an agency “need not—indeed cannot—base its
    every action upon empirical data” and may, “depending upon
    the nature of the problem, . . . be ‘entitled to conduct . . . a
    general analysis based on informed conjecture.’” 
    Id.
     (quoting
    Melcher v. FCC, 
    134 F.3d 1143
    , 1158 (D.C. Cir. 1998)). Here,
    the Commission highlighted a plausible conflict of interest: the
    potential misuse of “sensitive SIP customer information of
    significant commercial value” by administrators that sell
    competing market data products. CT Plan Order, 86 Fed. Reg.
    at 44,195–96 (quoting Governance Order, 85 Fed. Reg. at
    28,722). In support, the Commission invoked its experience in
    overseeing the existing Equity Data Plans as well as industry
    comments supporting the separation of the plan administrator’s
    regulatory responsibilities from an exchange’s commercial
    26
    interests. See id. at 44,195–96; Governance Order, 85 Fed. Reg.
    at 28,722–23. We have found this reasoning sufficient in the
    past. See Stilwell v. Off. of Thrift Supervision, 
    569 F.3d 514
    ,
    519 (D.C. Cir. 2009) (sanctioning agency’s reliance on its
    “long experience of supervising” regulated entities and
    “support in various comments submitted in response to the
    proposed rule”); Am. Great Lakes Ports Ass’n v. Schultz, 
    962 F.3d 510
    , 516 (D.C. Cir. 2020) (“A degree of agency reliance
    on [comments from affected parties] is not only permissible but
    often unavoidable.” (alteration in original) (quoting Nat’l Ass’n
    of Regul. Util. Comm’rs v. FCC, 
    737 F.2d 1095
    , 1124 (D.C.
    Cir. 1984))); cf. FCC v. Nat’l Citizens Comm. for Broad., 
    436 U.S. 775
    , 814 (1978) (permitting agencies to rely on
    “deductions based on the expert knowledge of the agency”
    (citation omitted)). That the Commission’s conflict of interest
    worry has not yet manifested itself is of little consequence, as
    an agency has the latitude to “adopt prophylactic rules to
    prevent potential problems before they arise”—that is, “[a]n
    agency need not suffer the flood before building the levee.”
    Stilwell, 
    569 F.3d at 519
    .
    Petitioners next fault the Commission for not extending
    the independent administrator requirement to non-SRO data
    vendors, even though those vendors sell market data products
    and could have similar conflicts of interest. See Pet’rs Br. 54–
    56. But “an agency need not target every danger in order to
    target any danger,” Am. Coal Co. v. Fed. Mine Safety and
    Health Rev. Comm’n, 
    796 F.3d 18
    , 29 (D.C. Cir. 2015), and
    instead “may marshal their limited resources by pursuing their
    goals ‘as priorities demand,’” 
    id.
     (quoting Nat’l Cong. of
    Hispanic Am. Citizens (El Congreso) v. Marshall, 
    626 F.2d 882
    , 888 (D.C. Cir. 1979)). Here, the Commission explicitly
    acknowledged that it “chose to address one substantial,
    inherent conflict of interest” in imposing the independent
    administrator requirement but permits the CT Plan operating
    27
    committee to “exercise discretion in selecting the new
    Administrator” in order to police other conflicts that may arise.
    CT Plan Order, 86 Fed. Reg. at 44,197. Although petitioners
    contend that non-SRO data vendors face “the exact same
    conflict” as SROs selling competing data products, see Pet’rs
    Br. 55 (emphasis omitted), the conflict is not the same because,
    as the Commission notes, the SROs have “sufficient voting
    power” and “incentive” to ensure that any non-SRO chosen to
    serve as administrator “would [not] face a financial conflict of
    interest and act as a direct competitor to the SROs’ proprietary
    data business,” CT Plan Order, 86 Fed. Reg. at 44,158, 44,197.
    Even if the CT Plan Order permits disparate treatment between
    SROs and representatives of non-SROs, the Commission has
    provided “a reasoned explanation” for such treatment.
    Burlington N. & Santa Fe Ry., 
    403 F.3d at 777
    .
    Third, and finally, petitioners assert that the Commission
    failed to consider whether “more good than harm will come”
    from an independent administrator requirement that excludes
    incumbent administrators that possess institutional knowledge
    and expertise—the NYSE and Nasdaq. See Pet’rs Br. 56–57
    (quoting Md. Peoples Counsel v. FERC, 
    761 F.2d 768
    , 779
    (D.C. Cir. 1985)); cf. Michigan v. EPA, 
    576 U.S. 743
    , 753
    (2015) (“[R]easonable regulation ordinarily requires paying
    attention to the advantages and the disadvantages of agency
    decisions.” (emphasis in original)). But the Commission
    acknowledged this argument in the CT Plan Order and
    reasoned that any loss in incumbent experience would be
    mitigated by the “broad range of financial service firms,
    unaffiliated with an SRO,” capable of serving as plan
    administrator and by the current administrators’ abilities to
    “advise and facilitate the onboarding process of the new
    Administrator.” CT Plan Order, 86 Fed. Reg. at 44,196–97. It
    further concluded any lingering “costs” resulting from a loss of
    expertise or experience are “justified because the inherent
    28
    conflicts of interest identified by the Commission . . . raise[]
    significant concerns regarding access to confidential subscriber
    information.” Id. at 44,197. Thus, we see no merit to
    petitioners’ argument that the Commission failed to consider
    the disadvantages or costs of the independent administrator
    requirement.
    D. Severability Vel Non
    Because we conclude that only one component of the
    Commission’s orders is invalid, there is the resulting question
    of severability. The APA defines “agency action” as “the whole
    or a part of an agency rule [or] order,” 
    5 U.S.C. § 551
    (13)
    (incorporated by 
    5 U.S.C. § 701
    (b)(2)), meaning that we are
    permitted to sever and set aside an offending portion while
    keeping intact the rest of the order. See Carlson v. Postal Reg.
    Comm’n, 
    938 F.3d 337
    , 351 (D.C. Cir. 2019); see also K Mart
    Corp. v. Cartier, Inc., 
    486 U.S. 281
    , 294 (1988). Severability
    turns on agency intent, meaning that “[w]here there is
    substantial doubt that the agency would have adopted the same
    disposition regarding the unchallenged portion if the
    challenged portion were subtracted, partial affirmance is
    improper.” Epsilon Elecs., Inc. v. U.S. Dep’t of Treasury, 
    857 F.3d 913
    , 929 (D.C. Cir. 2017) (quoting North Carolina v.
    FERC, 
    730 F.2d 790
    , 795–96 (D.C. Cir. 1984)). Further, we
    ask whether the remaining parts of the agency action can
    “function sensibly without the stricken provision.” Carlson,
    938 F.3d at 351 (quoting Sorenson Commc’ns Inc. v. FCC, 
    755 F.3d 702
    , 710 (D.C. Cir. 2014)). Here, we decline to sever with
    respect to the CT Plan Order—and thus vacate the order in its
    entirety. Regarding the antecedent Governance Order, we sever
    only the provision requiring petitioners to provide for non-SRO
    representation on the operating committee of any proposed
    plan and uphold the remainder of the Governance Order.
    29
    As to the CT Plan Order, the Commission made clear that
    its principal focus was replacing the three Equity Data Plans
    with a single, consolidated NMS plan that included the three
    Commission-recommended governance features. See CT Plan
    Order, 86 Fed. Reg. at 44,142–43; see also Proposed
    Governance Order, 85 Fed. Reg. at 2,182. In fact, the
    Commission evinced little regard for the rest of the CT Plan,
    stating that terms “not directed by the Governance Order” were
    within the control of the SROs, subject to Commission review
    and approval. CT Plan Order, 86 Fed. Reg. at 44,143. We
    therefore have “substantial doubt[s]” that the Commission
    would have permitted the CT Plan to be implemented in a
    piecemeal fashion and absent the provision requiring non-SRO
    representation on the operating committee, one of only three
    features the Commission required all SRO-proposed plans to
    include. See Epsilon, 857 F.3d at 929; see also Sierra Club v.
    FERC, 
    867 F.3d 1357
    , 1367 (D.C. Cir. 2017) (finding
    “substantial[] doubt” agency would have conducted piecemeal
    environmental review of pipeline project when it had
    previously “treated the project as a single, integrated
    proposal”).
    Moreover, permitting the remaining provisions of the CT
    Plan to take effect raises the question whether the CT Plan
    could “function sensibly.” Carlson, 938 F.3d at 351 (quoting
    Sorenson Commc’ns, 755 F.3d at 710). For example, the CT
    Plan, as proposed and approved by the Commission, requires
    that representatives of non-SROs hold one-third of the voting
    power on the committee and that committee approval under its
    “augmented majority” voting structure requires a “two-thirds
    majority of all votes on the operating committee” alongside “a
    majority of the SRO . . . votes.” CT Plan Order, 86 Fed. Reg.
    at 44,165; see also id. at 44,213 (CT Plan § 4.3(b)). Yet, if we
    were to invalidate the non-SRO representation provision and
    leave the remainder of the CT Plan intact, that would result in
    30
    simultaneously requiring both a two-thirds and a simple
    majority vote of approval by the SROs alone. This one example
    highlights how the challenged features of the CT Plan are
    “intertwined” in such a way that makes severance problematic.
    See Epsilon, 857 F.3d at 929 (quoting Davis Cty. Solid Waste
    Mgmt. v. EPA, 
    108 F.3d 1454
    , 1459 (D.C. Cir. 1997)).
    The Commission, for its part, pays little more than lip
    service to our concern that severing parts of the CT Plan Order
    would render the plan unworkable. It first makes the
    unsupported statement that, if one of the challenged provisions
    of the CT Plan is found to be unlawful, “the remaining
    provisions could ‘function sensibly.’” Resp’t Br. 56 (quoting
    Carlson, 938 F.3d at 351–52). As explained above, we struggle
    to see how that is the case. The Commission then invokes the
    severability provision included in the CT Plan itself, which
    states that “any determination that any provision of the CT Plan
    is invalid or unenforceable shall not affect the validity or
    enforceability of any other provisions of the CT Plan, all of
    which shall remain in full force and effect.” CT Plan Order, 86
    Fed. Reg. at 44,207. But “the ultimate determination of
    severability will rarely turn on the presence or absence” of a
    severability clause. Cmty. for Creative Non-Violence v. Turner,
    
    893 F.2d 1387
    , 1394 (D.C. Cir. 1990) (quoting United States v.
    Jackson, 
    390 U.S. 570
    , 585 n.27 (1968)). Instead, we look to
    agency intent and whether the valid portions can function
    absent the invalid portions, id.; doing so, we conclude that the
    CT Plan, as currently constructed, would be unworkable if we
    simply severed the provision requiring non-SRO
    representation.
    As to the Governance Order, it does not commit the
    Commission to any particular NMS plan or plan feature and is
    instead “no more than a call for a proposal that would then be
    subject to further notice, comment, and revision.” Nasdaq, 1
    31
    F.4th at 37; see also Order Denying Stay, 
    85 Fed. Reg. 36,921
    ,
    36,922 (June 18, 2020) (describing Governance Order as “first
    step toward establishing a new governance structure”). It was
    based on its lack of finality that we dismissed as premature
    petitioners’ earlier challenge to the Governance Order. Nasdaq,
    1 F.4th at 39. In line with this understanding of the Governance
    Order, we see no need to vacate those portions that direct the
    SROs to include plan features we have found permissible. We
    therefore sever only those parts of the Governance Order
    directing petitioners to include non-SRO representation in its
    proposed plan, leaving the remainder in place.
    For the foregoing reasons, we grant the petitions for
    review as to the inclusion of non-SROs on the CT Plan’s
    operating committee as voting members and vacate the CT
    Plan Order in its entirety. With respect to the Governance
    Order, we vacate only those portions authorizing the invalid
    non-SRO representation, leaving the remainder of the
    Governance Order intact.
    So ordered.