California Enacts Uniform Antitrust Pre-Merger Notification Act

State antitrust enforcers have taken a more active role in recent years. As tracked in our updated Healthcare Merger Matrix, the number of states implementing or considering expanding antitrust laws targeting proposed transactions continues to rise.¹ For instance, on July 27 and August 6, 2025 Washington and Colorado, respectively, enacted premerger notification laws (commonly referred to as "Mini HSRs" or "Baby HSRs") based on the Uniform Antitrust Pre-Merger Notification Act ("Uniform Act").²

Most recently, Governor Gavin Newsom signed the California Uniform Antitrust Premerger Notification Act ("SB 25") into law on February 10, 2026, making California the third state to implement a Mini HSR requirement.³ Beginning January 1, 2027, SB 25 will require certain merging parties to submit a copy of their federal HSR filing to the California Attorney General ("AG"). Unlike the federal HSR law, SB 25 does not impose a waiting period that parties must observe before closing. It is a notice requirement that will run parallel to the HSR waiting period.

Specifically, SB 25 requires HSR filers to submit a complete electronic copy of the HSR form with the AG contemporaneously with the federal filing (at the latest, within one business day of the federal filing) if either of the following applies:

1. the filer has its principal place of business in California; or
2. the filer, or an entity it directly or indirectly controls, had annual net sales in California of the goods or services involved in the transaction of at least 20 percent of the HSR size of transaction filing threshold (based on the 2026 filing thresholds,⁴ at least $26.78 million).

If an HSR filing party's principal place of business is in California, such filer must submit to the AG a copy of its HSR form and any additional documentary materials filed under the HSR Act and the AG may impose a $1,000 filing fee. If the HSR filing party's obligation to file is triggered by meeting California's sales threshold, then such filer is only required to submit a copy of its HSR form and may be required to submit the additional materials at the request of the AG. The AG may impose only a $500 filing fee for a filing based on the sales threshold. Failure to comply with SB 25 may subject parties to a civil penalty of $25,000 per day.

SB 25 provides robust confidentiality protections consistent with the HSR Act. The confidentiality protections prohibit the AG from making the HSR form public, exempt these materials from disclosure under California's public records law, and permit disclosure only under protective order in an administrative or judicial proceeding where the proposed merger is relevant. However, under SB 25, the AG may share information with the Federal Trade Commission and the United States Department of Justice Antitrust Division. After providing at least five business days' advance notice to the filing party, the AG may also share information with other states that have adopted the Uniform Act or substantively equivalent legislation as long as the other state's act included confidentiality provisions at least as protective as the confidentiality provisions of the Uniform Act.

Footnotes

1. State Healthcare Transaction Laws, Sheppard, https://discover.sheppardmullin.com/state-healthcare-transaction-laws/p/1.

2. Wash. Rev. Code § 19.420 (2025); 2025 Colo. Sess. Laws 2366.

3. SB 25

4. The 2026 HSR filing thresholds will go into effect on February 17, 2026.

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