California has joined the growing number of states adopting their own premerger-notification regimes. On February 10, 2026, Governor Newsom signed SB 25, the California Uniform Antitrust Premerger Notification Act, requiring certain parties making federal Hart-Scott-Rodino (HSR) filings to submit a copy of that filing to the California Attorney General.[1] The law applies to premerger notifications filed on or after January 1, 2027.[2] For dealmakers, the significance is practical.