The first quarter of 2026 has seen significant developments for M&A transactions that require a filing under the Hart–Scott–Rodino (HSR) Act. To comply with the HSR Act, transacting parties must notify the U.S. Department of Justice, Antitrust Division (DOJ) and the U.S. Federal Trade Commission (FTC) of their intended transaction if certain thresholds are met. In the past year, the rules and requirements for those notifications were greatly expanded, and then just in the past few months, challenged, overturned and now pending appeal.

HSR Rules Overturned

Enacted in 1976, the HSR Act sets forth the thresholds for when transacting parties must file premerger notifications with the federal antitrust agencies. In October 2024, the FTC issued a Final Rule adopting the most extensive revisions to the HSR Rules since the HSR Act’s original enactment. The Final Rule, which went into effect in February 2025, substantially expanded the prior rule by requiring parties to submit significantly more information and documents than previously required. According to the FTC, the new filing requirements were expected to increase the time required to complete a premerger filing by more than 60 hours on average and by more than 100 hours for more complex transactions. These predictions came to fruition and the time, and cost, to complete an HSR filing more than tripled in many cases.

On February 12, 2026, a year after the Final Rule went into effect, a federal court vacated the FTC’s Final Rule in Chamber of Commerce v. FTC, finding that the Final Rule exceeded the FTC’s statutory authority (Case No. 6:25-cv-9-JDK). The FTC has since filed an appeal with the Fifth Circuit Court of Appeals. While the Fifth Circuit initially granted the FTC a temporary administrative stay, the court ultimately denied the FTC’s motion for a stay pending appeal on March 19, 2026.

Following that decision, the FTC, through its Premerger Notification Office (PNO), confirmed that it is now accepting HSR filings using the Form and Instructions that were in place before the Final Rule went into effect. Despite the New Rules being vacated in their entirety, the PNO also said that it will continue to accept filings submitted under the February 10, 2025 Form and Instructions if parties voluntarily choose to use them.

Returning to the pre-February 2025 HSR Form and Instructions will reduce both the cost and amount of time necessary to submit an HSR filing to the FTC because it requires entities to conduct less data collection and produce fewer documents.

The appeal of the federal district court’s decision is still pending at this time, meaning the vacating of the 2025 HSR Form and Instructions could be reversed; although, this does not appear likely. The FTC and DOJ have already released a Request for Public Comment to collect information regarding the efficacy of the New Rules and other potential disclosure obligations. Some expect a new version of the Rules could be released as early as the end of this year.

U.S. Department of War to Review Defense-Related Transactions

The FTC has recently published guidance that certain transactions that are notifiable under the HSR Act will also need to be proactively disclosed to the U.S. Department of War (DOW) going forward. The DOW’s Office of Industrial Base Policy has published additional guidance, setting forth the four scenarios under which a transaction must be reported to the DOW:

1. Defense Directed Business. One or more of the parties has had, currently has or intends to have a contract with the DOW, or to perform as a subcontractor on a DOW contract.
2. Critical Technologies. The transaction involves technology related to one of the following:
   (i) Applied Artificial Intelligence;
   (ii) Biomanufacturing;
   (iii) Contested Logistics Technologies;
   (iv) Quantum and Battlefield Information;
   (v) Scaled Hypersonics; or
   (vi) Scaled Directed Energy.
3. Defense Industrial Base Sector. The transaction involves the research and development, or the design, production, delivery or maintenance, of military weapons systems, subsystems and components or parts. (Visit here for more information on the Sector.)
4. Intellectual Property. One or more of the parties has patents, trademarks, copyright protections or trade secrets relating to the above Critical Technologies or Defense Industrial Base Sector categories.

This marks a shift from prior practice, where the DOW typically requested HSR materials for transactions in which it had an interest. As of this new guidance, parties must affirmatively email the DOW, M&A Division, to inform the DOW about a transaction that requires premerger review and confirm that the parties have filed such HSR notification. These notifications should be submitted concurrently with the transaction’s standard HSR filing.

While a brief analysis must be conducted in advance of each HSR filing to determine whether the parties must notify the DOW, this new requirement will not impose an additional waiting period on the transacting parties, nor does it require that any additional fees be paid. Because the requirement is new, it remains unclear how actively the DOW will use these notifications to identify transactions for further review.

California, Indiana and Other States to Require HSR Filings

California has joined Colorado and Washington as the third state to require the submission of HSR filings to the State Attorney General following the passage of state legislation. Indiana’s version of the similar requirement will likely go into effect prior to California’s, but technically, it has not yet been signed into law. These states have primarily adopted statutory language mirroring the Uniform Antitrust Pre-Merger Notification Act (UAPNA) in statutes that are colloquially referred to as “mini-HSR Acts.”

The filing requirement in California will apply to any HSR filings made to the FTC and DOJ on or after January 1, 2027. Indiana’s bill is drafted to go into effect for all filings made after June 29, 2026. As in Washington and Colorado, a filing will be required only if a party has its principal business in the relevant state or annual net sales in the state greater than approximately $26.78 million. If either threshold is met, the HSR form must be submitted to the State Attorney General promptly after filing HSR—within one business day for California and contemporaneously in Indiana. Noncompliance can result in civil penalties that vary by state, but California has the highest of up to $25,000 per day after written notice and a three-business day period to cure.

More states will likely follow in the footsteps of California, Indiana, Colorado and Washington. So far, Hawaii, New York, West Virginia and Washington, D.C., have taken steps to enact mini-HSR Acts. Notably, New York’s proposed legislation would be even more expansive, likely requiring significantly more notifications than California, Colorado or Washington, which more closely followed the UAPNA. New York’s mini-HSR Act, as drafted, would require any entity that conducts business within New York to submit its HSR form to the New York Attorney General, forgoing a revenue threshold such as those that exist in the other statutes. State filing requirements generally are not expected to materially increase filing costs, nor do they affect the federal 30-day waiting period necessary under the HSR Act. The primary intention for states in requiring the submission of HSR filings is to gain access to information that is otherwise confidential to assess transactions that could affect commerce within the state. Transacting parties should be aware that states may seek to challenge transactions they believe could substantially lessen competition, including by coordinating with the DOJ or FTC or filing their own lawsuit. A coalition of 13 states have moved to block the merger between Nexstar Media Group and Tegna, despite the FTC and DOJ clearing the transaction under the HSR Act. A federal judge has issued a preliminary injunction to pause the merger while the lawsuit proceeds. State-led actions like these are likely to increase as more mini-HSR Acts promulgate.

Parties should involve sophisticated antitrust counsel early to navigate these myriad changes and assess whether additional notification obligations or related enforcement risk may apply to their transactions.

Private Equity Report Spring 2026, Vol 26, No 1