The United States maintains one of the most active merger control regimes in the world, centered on the Hart-Scott-Rodino Antitrust Improvements Act of 1976. The federal statute requires parties to certain transactions to notify the government before closing, giving regulators time to investigate potential anticompetitive effects. The notification and filing requirements are implemented by the Federal Trade Commission and the Department of Justice’s Antitrust Division through regulations in Title 16 of the Code of Federal Regulations.
Parties generally must file a notification if they meet specific size thresholds. The HSR Act covers the acquisition of both controlling and non-controlling equity interests, as well as acquisitions of assets like exclusive licenses. The filing obligation depends on whether the “size of transaction” and “size of persons” tests are satisfied. Acquiring a minority stake is reportable if the buyer does not intend to be a passive investor and the size tests are met. Conversely, acquiring 10% or less of voting securities is exempt for passive investors.
Joint ventures require the creation of a new entity and are reportable under the same size tests. Acquisitions of assets and prospective financial instruments like options are also subject to the rules. Linked or successive steps between the same parties are treated as one transaction, meaning parties must notify if the material terms change after an initial filing. This creates a risk that a deal initially below the threshold might become reportable if the parties alter the structure significantly.
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While the FTC and DOJ have historically operated independently, the administration in power influences policy direction through presidential appointments and leadership changes. This political alignment means merger control reviews often reflect the priorities of the current executive branch. The Regulators can challenge any transaction through other antitrust laws, including sections 7 of the Clayton Act and section 2 of the Sherman Act, regardless of whether an HSR filing was made.
State-Level Filing Obligations
Several states have adopted their own “mini-HSR” laws, creating a patchwork of filing requirements. California, Colorado, Indiana, and Washington currently have these laws in effect or scheduled to take effect soon. A party must submit a courtesy copy of its federal HSR filing to the relevant state attorney general if it has its principal place of business in that state or if it generated in-state revenues of at least 20% of the minimum federal size-of-transaction threshold in the previous fiscal year. These obligations apply independently to each party involved in the transaction.
Almost all states require pre-merger filings for healthcare transactions occurring within their borders. State attorneys general have the power to investigate and challenge mergers, often joining federal regulators in enforcement actions and occasionally bringing challenges on their own. This parallel enforcement structure means a deal might pass federal review but face hurdles in multiple state jurisdictions.
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Updates and Foreign Investment
The regulatory environment for merger control is in flux. In February 2025, the FTC implemented major changes to the HSR Rules and filing form, but a Federal District Court vacated those changes in February 2026. The Regulators subsequently issued a Request for Information seeking public comment on the vacated form. This signals a two-track strategy for future rulemaking: regulators aim to reduce burdens for non-problematic transactions while expanding the reach of the HSR Act. Any new rules are unlikely to take effect before 2027.
Transactions involving military elements or certain economic sectors must also be reported to the Department of Defense. Beyond antitrust, the United States maintains a separate foreign direct investment regime for national security concerns administered by the Committee on Foreign Investment in the United States (CFIUS). This separate review process can apply to mergers and acquisitions even if they do not trigger HSR filing requirements, adding another layer of scrutiny for cross-border deals.
Thresholds and Valuation
The thresholds for mandatory filing are updated annually in the spring. These tests measure the value of the transaction against the size of the parties involved. If the smaller party is not engaged in manufacturing, it meets the size of person test only if its total assets exceed $26.8 million. Asset acquisitions must be aggregated if the acquiring party has a signed letter of intent or agreement in principle to acquire assets from the same acquired person within the previous 180 days.
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For foreign-to-foreign transactions, the rules provide specific exemptions. An acquisition of foreign assets is exempt unless those assets generated more than $133.9 million in sales into the United States. Similarly, the acquisition of a foreign target by a foreign buyer is exempt unless the target holds U.S.-based assets valued at $133.9 million or made aggregate sales in or into the U.S. of over $133.9 million in its most recent fiscal year. These exemptions are highly fact-specific and require careful analysis.
The value of assets acquired is generally the fair market value, though if a higher purchase price is determined, that figure is used instead. Parties must rely on the Interbank Exchange Rate for currency conversions. Assets relevant for HSR purposes must be located in the United States, and exclusive licenses are treated as asset acquisitions that must generate revenue in the U.S. to be reportable.