United States

The Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (15 U.S.C. § 18a) (the “HSR Act”). The notification and filing requirements are implemented pursuant to the Premerger Notification Rules (the “HSR Rules”) promulgated by the Federal Trade Commission (FTC) and the Department of Justice’s Antitrust Division (DOJ) (together, the “Regulators”) as Parts 801, 802, and 803 of Title 16 of the Code of Federal Regulations (CFR).

Question 5, below, describes substantive antitrust enforcement legislation.

Mandatory and suspensory.

The Regulators investigate mergers and decide whether to challenge mergers in court.

State attorneys general may also investigate and challenge mergers. They often join the Regulators in bringing challenge and occasionally bring challenges on their own.

While historically considered independent, legally with respect to the FTC and in practice with respect to the DOJ, presidential appointments and leadership changes have increasingly brought merger control reviews within the policy direction of the administration.

Economy-wide. The United States maintains a foreign direct investment filing regime for transactions that impact or relate to national security (i.e., the Committee on Foreign Investment in the United States or CFIUS). Transactions involving military elements and/or certain economic sectors must also be reported to the Department of Defense (DoD).

The HSR Act is the federal merger control statute.

Some states have adopted “mini-HSR” laws: California (effective January 1, 2027), Colorado (currently in effect), Indiana (effective July 1, 2026), and Washington (currently in effect). Qualifying parties who have: (i) filed under the HSR Act; and (ii) a prescribed nexus to the state must share a courtesy copy of their HSR Act filing with the state’s attorney general.

All but 13 states have pre-merger filing obligations for healthcare transactions occurring within their borders.

The Regulators are empowered to cooperate with foreign antitrust regulators on multinational merger reviews, with filed information kept confidential unless the filing party waives such protection.

In February 2025, the FTC implemented major changes to the HSR Rules and the form used to notify transactions to the Regulators. These changes were vacated by a Federal District Court in February 2026. In March 2026, the Regulators issued a Request for Information seeking public comment on the vacated form, signaling a two-track strategy in the next rulemaking seeking to reduce burdens for clearly non-problematic transactions while expanding the HSR Act’s reach. Any new rules would not take effect prior to 2027.

The HSR Act covers the acquisition of both controlling and non-controlling equity interests, as well as acquisitions of assets (including certain exclusive licenses). Generally, parties must file if the “size of transaction” and “size of persons” tests are satisfied (Question 3.1, below, provides the thresholds for these tests).

The acquisition of a minority stake in a corporation (i.e., the acquisition of shares entitling the holder to vote for the election of directors) is reportable if the acquiring person does not intend to be purely passive and the size of transaction and size of persons tests are both satisfied. The acquisition of 10% or less of a corporation’s voting securities may be exempt if the acquiring person intends to be a passive investor.

The acquisition of a minority stake in a non-corporate entity (e.g., limited partnership, limited liability company) is not reportable if the acquiring person will not have the right to 50% of the profits or assets upon dissolution.

Yes.

Acquisitions of controlling interests (e.g., stock that allows the holder to vote for the election of directors, limited liability company interests entitling the holder to 50% or more of the entity’s profits or assets upon dissolution) may be reportable if the size of transaction and size of persons tests are both met. Acquisitions of assets (including exclusive licenses) may be reportable if the size of transaction and size of persons test are satisfied.

Acquisitions of prospective financial instruments (e.g., options, warrants, convertible debt structures) that do not entitle the holder to vote for the election of directors are not reportable. However, a filing obligation may be triggered on exercise or conversion.

Acqui-hire transactions may be reportable if the motivation for structuring the transaction in that form is to avoid otherwise having to file.

A joint venture requires the creation of a new entity and is reportable if:

• one party has annual net sales or total assets of USD 267.8 million or more, another party has annual net sales or total assets of USD 26.8 million or more, and the joint venture entity will have total assets of USD 26.8 million or more; or
• one party has annual net sales or total assets of USD 26.8 million or more, another party has annual net sales or total assets of USD 26.8 million or more, and the joint venture entity will have total assets of USD 267.8 million or more.

Commercial relationships that involve neither the creation of a new entity nor exclusive licensing are not reportable.

Linked or successive steps between the same parties are generally treated as the same transaction. If those steps change in a material way after filing, the parties will need to notify the Regulators. The Regulators may then require the parties to file again, which would result in the payment of another filing fee and observance of another waiting period.

Interrelated transactions between different parties are treated as separate transactions and must be reported accordingly.

Generally, parties must file if the “size of transaction” and “size of persons” tests are satisfied. These threshold tests are:

• the size of the transaction is greater than USD 535.5 million; or
• the size of the transaction is greater than USD 133.9 million but less than USD 535.5 million; and
  • one party has annual net sales or total assets of USD 26.8 million or more; and
  • the other party has annual net sales or total assets of USD 267.8 million or more.

If the smaller party is not engaged in manufacturing, then it meets the size of person test only if its total assets are USD 26.8 million or more.

Acquisitions of additional voting securities in corporations must be aggregated with current holdings and may be reportable if the following thresholds are met:

• greater than USD 133.9 million but less than USD 267.8 million;
• equal to or greater than USD 267.8 million but less than USD 1.339 billion;
• equal to or greater than USD 1.339 billion but less than USD 2.678 billion;
• greater than USD 2.678 billion and representing 25% or more, but less than 50%, of the corporation’s total voting securities issued and outstanding; and
• 50% or more and having a total value of greater than USD 133.9 million.

“Voting securities” are equity that entitle the holder to vote for the election of members of the corporation’s board of directors.

These thresholds are not applicable to non-corporate entities (i.e., limited liability companies, limited partnerships). An acquisition of interests in a non-corporate entity is reportable only if the size of transaction is greater than USD 133.9 million and the acquiring person will have the right to 50% of the profits or assets upon dissolution.

Asset acquisitions must be aggregated if the acquiring person (i) has a signed letter of intent or agreement in principle to acquire assets and (ii) within the previous 180 days has acquired assets or signed a letter of intent or agreement in principle to acquire additional assets from the same acquired person.

The mini-HSR obligations described in Question 1.5 apply independently to each party. A party must submit a courtesy copy of their HSR Act filing to the relevant state attorney general if either: (i) the party has its principal place of business (i.e., its headquarters) in the state or (ii) the party had in-state revenues in its previous fiscal year from the goods or services involved in the transaction of at least 20% of the minimum HSR Act size-of-transaction threshold (i.e., 20% of USD 133.9 million or USD 26.78 million).

Parties may be required to submit copies of their HSR Act filings to the DoD if either party:

• has a history of or intent to contract with the DoD or a prime DoD contractor;
• is involved in one of the six critical technologies vital to U.S. national security;
• is involved in one of the DoD’s Defense Industrial Base critical infrastructure sectors; or
• has intellectual property related to the critical technologies or critical infrastructure sectors.

All dollar value thresholds for the HSR Act are updated annually in the spring and published on the FTC’s website (see www.ftc.gov/enforcement/premerger-notification-program/current-thresholds) and in the Federal Register (see www.federalregister.gov).

Not applicable.

Assets relevant for HSR Act purposes must be located in the United States. Exclusive licenses, which are treated as acquisitions of assets, must generate revenue in the United States.

The value of assets to be acquired is the fair market value of the assets, or, if determined and greater than the fair market value, the acquisition price.

Use the Interbank Exchange Rate and rely on the following guidelines:

• Annual statement of income: average exchange rate for the year reported.
• Regularly prepared balance sheet: exchange rate in effect for the date on the balance sheet.
• Pro forma balance sheet: exchange rate for the date the pro forma balance sheet was created.
• Acquisition price: exchange rate for the date of closing.
• Fair market value: exchange rate for the date fair market valuation is determined.
• Market price: when necessary, use daily exchange rate to ascertain the lowest closing quotation or lowest closing bid price for the relevant days.

Not applicable.

Foreign-to-foreign transactions are reportable under the HSR Act, subject to exemptions provided in 16 C.F.R. §§ 802.50 and 802.51.

Under 16 C.F.R. § 802.50, the acquisition of foreign assets is exempt from reporting unless the foreign assets to be acquired generated more than USD 133.9 million of sales in or into the United States. If the foreign assets exceeded USD 133.9 million in sales, the transaction may still nevertheless be exempt if:

• both parties are foreign;
• the aggregate sales of both parties in or into the United States are less than USD 294.5 million in their respective most recent fiscal years;
• the aggregate total assets of the parties located in the United States, subject to certain exemptions, are less than USD 294.5 million; and
• the transaction is valued less than USD 535.5 million.

Under 16 C.F.R. § 802.51, the acquisition of a foreign target by a foreign buyer is exempt from reporting unless the acquisition will confer control of the target and the targets holds United States-based assets, subject to certain exemptions, having an aggregate total value of USD 133.9 million or made aggregate sales in or into the United States of over USD 133.9 million in its most recent fiscal year. If the foregoing is true, the transaction may nevertheless be exempt if:

• both parties are foreign;
• the aggregate sales of the parties in or into the United States are less than USD 294.5 million in their respective most recent fiscal years;
• the aggregate total assets of the parties located in the United States, subject to certain exemptions, are less than USD 294.5 million; and
• the transaction is valued less than USD 535.5 million.

Exemptions to the notification obligations of the HSR Act, listed in 16 C.F.R. § 802 et al., are highly fact specific.

The Regulators are empowered to challenge any transaction through other antitrust laws (e.g., section 7 of the Clayton Act, section 2 of the Sherman Act).

The Regulators are empowered to investigate and challenge non-reportable transactions through other antitrust laws (e.g., section 7 of the Clayton Act, section 2 of the Sherman Act).

See Questions 4.2 and 4.12, below, for the Regulators’ timeline to review HSR-reportable transactions. Though highly unusual, the Regulators may sue to stop a transaction after expiration of the suspensory waiting period.

No.

Notification is mandatory if the thresholds are met. Fact-specific exemptions are provided under 16 C.F.R. § 802 et al.

Filing initiates a waiting period lasting 30 calendar days, or 15 calendar days if the transaction is a cash tender offer or in connection with a bankruptcy.

During the waiting period, the parties may not close but may engage in other activities that do not constitute gun-jumping (e.g., integration planning).

The parties may elect to seek early termination of the waiting period. The Regulator’s decision on whether and when to grant early termination is discretionary.

A complete HSR Act notification is composed of two parts: the A-Side, submitted by the buyer or licensee, and the B-Side, submitted by the seller or licensor.

Yes, there is a filing fee with the amount owed based on the size of the transaction:

• not less than USD 133.9 million but less than USD 189.6 million: USD 35,000;
• not less than USD 189.6 million but less than USD 586.9 million: USD 110,000;
• not less than USD 586.9 million but less than USD 1.174 billion: USD 275,000;
• not less than USD 1.174 billion but less than USD 2.347 billion: USD 440,000;
• not less than USD 2.347 billion but less than USD 5.869 billion: USD 875,000; and
• USD 5.869 billion or more: USD 2.46 million.

By default, the fee is owed by the buyer; however, the parties are free to split or otherwise assign the fee to the seller.

The notification will not be accepted, and the waiting period will not begin to run, until the Regulators have received both the filing fee and the A-Side and B-Side filings.

The filing fee amounts and corresponding ranges are updated annually in the spring on the FTC’s website and in the Federal Register (see Question 3.1, above).

Notification can be made either under a signed agreement or a sufficiently detailed term sheet.

There is no statutory deadline for filing.

The prescribed form for notifications is available on the FTC’s website.

The form requires the parties to:

• describe themselves and the transaction;
• submit agreements, financial statements, and transaction-related competitive analyses;
• disclose corporate information, including U.S. revenues, subsidiaries, and certain minority shareholders and investments; and
• provide additional geographic information relating to overlapping revenues (and for the acquiring person, certain prior acquisitions and information about associates (i.e., entities the acquiring person is under common control or investment management with)).

The filing requires two signatures, both under penalty of perjury: (i) a certification that the contents of the filing are true and correct; and (ii) a declaration that the filing party has a present good faith intention to complete the transaction described in the filing.

No.

Pre-notification discussions are not required. The parties may reach out to the Regulators before or after filing for voluntary discussions or to voluntarily produce explanatory documents.

See Question 4.2, above, regarding the waiting period and Question 4.3 regarding early termination of the waiting period.

At any time prior to the expiration or early termination of the waiting period, the Regulators may issue a request for additional information known as a “Second Request.” A Second Request stops the initial waiting period and requires the parties to gather additional documents and responses in satisfaction of demands made by the Regulators. Once the parties certify to “substantial compliance” in responding to those demands, a second 30-day waiting period begins.

The waiting period cannot begin, or expire or be earlier terminated, on a weekend or a day the banks of the United States are closed. In both instances, the relevant date is pushed to the next business day.

Approximately one and a half months: 10 business days from signing to prepare and submit the filings, followed by the 30-day waiting period.

A notification to report an all-cash tender offer triggers a 15-day waiting period.

The Regulators are entitled to collect information from other industry participants in reviewing the filings.

See Question 4.8, above, on documents required to be provided and Question 4.12, above, on second requests.

All documents and information provided to the Regulators are kept confidential and exempted from disclosure under the Freedom of Information Act (FOIA).

In the United States, the core substantive legality test for merger reviews is under Clayton Act §7: whether “the effect” of the acquisition “may be substantially to lessen competition, or to tend to create a monopoly.” See 15 U.S.C. § 18. Unlike the EU or UK, the U.S. does not employ a two-phase administrative process: regulators apply the same standard throughout the process, though the FTC and DOJ conduct initial and then more in-depth reviews as needed. Proposed transactions in regulated industries may also be subject to concurrent investigations by sectoral regulators (e.g., Federal Communications Commission, Federal Energy Regulatory Commission) that have separate competition authority, typically contained in the agency’s enabling statute.

The HSR process is critical to helping the Regulators initially determine whether a proposed transaction will violate the U.S. antitrust laws by substantially lessening competition or creating a monopoly. The HSR filings, early negotiations, engagement with Regulators, and requests for additional information (“Second Requests”) are designed to provide the Regulators with the information they need to evaluate the legality of a proposed transaction.

In practice, as outlined in the 2023 Merger Guidelines, the recurring competition concerns are loss of substantial competition between companies (including effects on price, quality, wages, or other competitive dimensions), increased risk of coordination among remaining firms (including collusion and tacit understanding), and deals that contribute to a trend toward concentration or vertical integration (including input and customer foreclosure concerns).

Merging parties may raise efficiencies as a defense or rebuttal to justify a merger, but the threshold is significant and difficult to successfully meet. The 2023 Merger Guidelines state that the Regulators will “not credit vague or speculative claims, nor will they credit benefits outside the relevant market that would not prevent a lessening of competition in the relevant market.” Instead, the Regulators will evaluate whether the proffered efficiencies are specific to the merger, verifiable, prevent a reduction in competition, and are not the result of the anticompetitive worsening of terms for the merged firm’s trading partners. This analytical framework rarely results in an agency or court accepting rebuttal evidence of claimed efficiencies to justify an otherwise anticompetitive transaction.

The 2018 CVS Health-Aetna merger illustrates how well-substantiated efficiency arguments can influence the Regulators’ assessments. In focusing on vertical efficiencies rather than horizontal market concentration, CVS argued that integrating Aetna’s insurance operations with its pharmacy and clinic network would yield transaction-specific, consumer-facing efficiencies, which the DOJ found did not raise significant competitive harm.

For transactions that are reportable under the filing thresholds, the HSR Form and accompanying documents comprise the first set of information provided to the Regulators about their proposed transaction. Parties typically provide the Regulators with an initial presentation, colloquially referred to as a “Day One presentation,” to present the merits of the transaction to agency staff.

If the Regulators have further questions or concerns about a proposed transaction, the merging parties typically have a chance to respond to those questions within the waiting period, or pull and refile their premerger notification before the initial 30-day waiting period expires to give the agency more time for review. Agency staff will issue voluntary access letters or Civil Investigative Demands seeking the production of documents, information, and data from the merging parties, as well as from third-party market participants to learn more about the industry and prevailing competitive dynamics.

The clearest formal signal of agency concern is the issuance of a Second Request. Complying with a Second Request typically takes months to accomplish and requires the production of millions of documents and a significant amount of data and information. This period also includes various forms of additional advocacy, including white papers and presentations to address the agency’s lingering questions or concerns.

Remedies may be proposed by the merging parties at any stage of the review process, though agency leadership has made clear that proposals should come early, as late-stage proposals may be rejected where there is insufficient time to evaluate their adequacy.

Before a Second Request is opened, parties may offer a “fix-it first” remedy — a structural solution implemented before the merger is consummated that, if accepted by the agency, eliminates the anticipated anticompetitive concerns and obviates the need for litigation. A fix-it first remedy may be inappropriate if it is presented after the agency has already determined that it has a substantial basis for filing a complaint or that any potential remedy would be inadequate.

During the investigation, parties may propose remedies to address competitive concerns identified by the agency prior to the filing of a complaint. In such cases, the Regulators will consider a consent decree (or FTC consent order) that allows the merger to proceed with modifications that preserve or restore competition.

After a complaint is filed, the agency may accept a proposed remedy and settle the lawsuit, or proceed first on liability and address remedies separately, including through continued negotiations or post-liability proceedings. At any stage, the Regulators are not obligated to accept proposed remedies and may instead seek to block a transaction where they conclude proposed relief would not fully address competitive concerns.

When the DOJ is the reviewing agency, consent decrees must be publicly filed along with a competitive impact statement and followed by a public comment period. The settlement must then be approved by a federal judge as being in the public interest pursuant to the Tunney Act process. See 15 U.S.C. §§ 16(b)–(h). When the FTC is the reviewing agency, negotiated remedies are formalized through an administrative consent process that provides for Commission approval and a public comment period before issuance of a final order. See 16 CFR § 2.34.

Currently, the DOJ and FTC prefer structural remedies over behavioral remedies in both horizontal and vertical mergers. See Fed. Trade Comm’n, Statement from FTC Chairman Andrew N. Ferguson, In the Matter of Synopsys, Inc./Ansys, Inc., at 7 (May 28, 2025) (Behavioral remedies are “often difficult or impossible for the Commission to enforce effectively […] They are therefore disfavored.”).

The Regulators subject proposed divestiture buyers and packages to a significant vetting process before granting approval. See Fed. Trade Comm’n., Keynote Address from FTC Commissioner Melissa Holyoak at the USC Gould/Analysis Grp. Glob. Competition Law Thought Leadership Conf., at 6 (June 5, 2025).

In the statement that accompanied the announcement of the settlement in Synopsys/Ansys, the Commission outlined some guiding criteria for what the agency is looking for in terms of an appropriate divestiture package. Structural remedies should generally involve the sale of a standalone or discrete business along with all tangible and intangible assets necessary to make the business viable and competitive, while eliminating ongoing entanglements with the merged firm. See Statement from FTC Chairman Andrew N. Ferguson, In the Matter of Synopsys, Inc at 7.

Once approved, the Regulators may also require compliance reporting and monitors, with staff carefully reviewing divestiture-related documents. See Keynote Address from FTC Commissioner Melissa Holyoak at 6–7. Regulators may also review consummated transactions and will seek a remedy that restores competition, including unwinding the transaction entirely or requiring divestiture of the acquired assets. See, e.g., In the Matter of Otto Bock HealthCare North Am., Inc., No. 9378, Final Order (F.T.C. Nov. 1, 2019) (requiring Otto Bock’s consummated, nonreportable acquisition of competitor Freedom Innovations to be unwound upon finding the transaction was anticompetitive).

Completion can occur before remedies have been fully implemented. Consent decrees contemplate this by giving parties a prescribed period to complete divestitures and imposing hold separate and asset preservation provisions to maintain the viability of the divested assets in the interim. See, e.g., In the Matter of Tronox Ltd, No. 9377, Decision (F.T.C. May 28, 2019) (allowing 30 days’ post-acquisition to complete the divestiture).

Compliance with consent decrees is overseen by the DOJ and by the FTC. Consent decrees must include monitoring provisions, bind all necessary parties, including successors and assigns, and incorporate standard provisions such as decree-term extensions upon violation. They may be enforced through federal courts, including contempt proceedings. A court- or Commission-appointed divestiture trustee may be nominated if a party fails to divest within the prescribed period.

Absent a grant of early termination, the Regulators will not contact the parties when the waiting period expires. If early termination is granted, then the FTC will email a confirmation to counsel and publish notice of the early termination grant on its website and in the Federal Register.

Second Requests are communicated by phone call or email to counsel.

Immediate effect.

The expiration of the HSR waiting period does not constitute agency approval of non-competes or other restraints included in transaction documents and does not bar later proceedings regarding the acquisition.

It is rare for the Regulators to investigate ancillary restraints after expiration of the HSR waiting period.

No.

The Regulators can impose a civil penalty of up to USD 53,088 per day. The acquiring person, including any natural persons, is typically sanctioned. For instance, in 2024, Ryan Cohen, managing partner of RC Ventures, LLC and Chairman and CEO of GameStop Corp., agreed to pay a USD 985,320 civil penalty to settle charges he failed to make a required HSR Act filing.

The Regulators can impose a civil penalty of up to USD 53,088 per day. For instance, in 2025, the FTC obtained a record USD 5.6 million civil penalty to settle allegations against three energy companies that they engaged in illegal gun-jumping.

The Regulators can impose a civil penalty of up to USD 53,088 per day in addition to seeking criminal sanctions.

The authors would like to thank Tommy Rucker, Shaina Vinayek and RaCia Poston for their assistance and contributions to this chapter.