United States: California Adopts Uniform Premerger Notification Law

In brief

California Governor Gavin Newsom has signed SB 25, the California Uniform Antitrust Premerger Notification Act. The Act requires parties submitting a federal Hart-Scott-Rodino (HSR) filing to provide a copy to the California Attorney General if they have sufficient ties to California. The new law takes effect on January 1, 2027.

California joins Washington¹ and Colorado² as the third state to adopt state-level premerger notification requirements, with more expected to follow. As with the Washington and Colorado statutes, the California law is not suspensory and does not impose any clearance requirement.

Key takeaways

California’s SB 25 mirrors Washington and Colorado premerger notification laws and, like theirs, is based on the Uniform Antitrust Pre‑Merger Notification Act (“Act”), giving state Attorneys General prompt access to HSR filings. It goes into effect on January 1, 2027.
California notification requirement: HSR filers must provide an electronic copy to the California AG within one business day of submitting the HSR filing if:
- The filing party’s principal place of business is in California; OR
- The filer (or a directly or indirectly controlled entity) had annual net sales in California of the goods or services involved in the transaction accounting for at least 20% of the lowest size-of-transaction HSR filing threshold.³
The California AG may impose maximum filing fees of up to USD 1,000 on a filing party with its principal place of business located in California and USD 500 on parties with annual net sales of at least 20% of the HSR filing threshold from sales in California.
The new law is non-suspensory and does not impose any additional waiting period or restrict the parties’ ability to close a transaction.
Compliance with California’s new law is critical. Following written notice and a three-business day cure period, the California AG may impose civil penalties of up to USD 25,000 per day for noncompliance.
Additional states are expected to follow as certain state AGs aim to take a more proactive approach with merger enforcement, including in New York, Hawaii, Indiana, West Virginia, and the District of Columbia.
Parties to transactions triggering an HSR filing obligation should incorporate state specific notification assessments into their HSR filing workflow.

In more detail

California has adopted the California Uniform Antitrust Premerger Notification Act, which creates another state-level premerger notification process for parties with a sufficient nexus to California that pursue a transaction requiring notification under the HSR Act. Colorado and Washington have adopted similar statutes, which are already in force. California’s law becomes effective January 1, 2027.

As with the Washington and Colorado legislation, the Act is based on the Uniform Antitrust Pre‑Merger Notification Act that was approved by the Uniform Law Commission in July 2024 and is intended to provide the California AG early access to federal HSR materials without imposing a separate state clearance requirement.

Washington state led the charge in this area — passing a similar version of the Act that went into effect in July 2025. Colorado followed soon thereafter, passing its premerger notification law that became effective in August 2025.

For transactions requiring an HSR filing, parties must now assess whether they are required to provide copies of their HSR filings to state attorneys general pursuant to state level premerger notification regimes — including California for filings made on or after January 1, 2027.

How it works

Each person filing an HSR premerger notification must evaluate whether it satisfies either of the California statute’s nexus requirements — being headquartered in CA or deriving revenue from relevant sales in California valued at 20% or more of the latest HSR size-of-transaction threshold. For those that do satisfy one or the other, they must submit a complete electronic copy of the HSR form to the California AG within one business day of filing with the federal antitrust agencies.

Filers who maintain a principal place of business in California must provide the California AG a complete electronic copy of any “additional documentary material” filed with the HSR form (which encompasses the exhibits to the HSR filing), in addition to a maximum filing fee of USD 1,000. Filers who meet the sales threshold must provide that additional documentary material within seven business days of receiving a request from the California AG, who may charge a maximum filing fee of USD 500. The material filed with the California AG includes confidentiality protections, including a requirement for the AG to provide a secure means to receive and store materials.

The new law is non‑suspensory — i.e., it does not impose a separate California waiting period — so parties are free to close a covered transaction without having to wait for the California AG to complete its review.

According to Attorney General Rob Bonta, SB 25 is intended to provide earlier access to HSR materials and facilitate coordination with federal enforcers, rather than expand required disclosures or introduce a new approval requirement before closing.⁴ Paula Blizzard, California’s Senior Assistant AG for the Antitrust Section, stated that California just wants to get the filings at the same time as the federal government and that “[t]he vast majority of mergers present no competition issues.”⁵ SAAG Blizzard emphasized that the purpose of California’s new “mini-HSR” regime is not intended to tack substantive state-level premerger notification requirements onto federal HSR filings and this is not a case “where the [California AG plans] to open 100 new merger cases.”⁶

However, the new Act does carry meaningful compliance consequences. After receiving written notice from the California AG and a three-business day period to cure, the AG may impose civil penalties up to USD 25,000 per day for failure to submit the required materials or timely respond to a request for additional documentary material.

Practical implications (what deal teams should do now)

Add SB 25 to HSR checklists for closings occurring after the start of 2027. The obligation is keyed to HSR filings and applies when parties have a sufficient California nexus, so companies should assess whether SB 25’s notification requirement is triggered (along with Washington’s and Colorado’s “mini HSR” statutes) as part of their HSR filing assessments.
Evaluate parties’ “California nexus” early in diligence. Confirm (i) principal place of business and (ii) whether annual net sales in California of the goods/services involved in the transaction meet the 20% of HSR threshold test.
Operationalize the “one business day” filing requirement. If required, ensure electronic copies of the parties’ HSR filings are delivered to the California AG within one business day of the HSR filing submission, and monitor California AG guidance on the secure filing mechanism.
Coordination with other California legal requirements may be necessary. While SB 25 applies to all transactions, California law imposes other requirements on parties to proposed transactions in certain industries. For example, transactions in the healthcare industry may trigger separate/different notification requirements under California law.

Even though the statute is framed as primarily informational, providing the California AG with access to HSR filings at the outset of federal review introduces an additional stakeholder and may complicate or prolong the HSR review process. Given the evolving requirements around state-level premerger notification, parties should consult with outside counsel and understand the potential state-level areas of concern in the earliest stages of any contemplated merger.

Ethan Primeaux, Law Graduate Fellow, contributed to this legal update.

In brief

Key takeaways

In more detail

How it works

Practical implications (what deal teams should do now)

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