State Mini-HSR Laws: Washington, Colorado and California Filings

State “mini-HSR” laws require companies that file a federal Hart-Scott-Rodino premerger notification to send a copy to a state attorney general when the deal has a local connection. As of November 2026, Washington and Colorado have such laws in force, and California’s takes effect for filings on or after January 1, 2027. The test is a principal place of business in the state or in-state sales of at least 20% of the HSR threshold.

All three states based their laws on the Uniform Antitrust Pre-Merger Notification Act, a model law from the Uniform Law Commission. The laws add no new waiting period and do not change the federal review. They give state antitrust enforcers the same filing the FTC and the Justice Department receive, at the same time, so the states can investigate deals that affect their markets.

Which states require a copy of the HSR filing?

Three states have enacted the uniform act, with differences in timing, fees and penalties.

Washington’s statute also applies to health care providers and provider organizations doing business in the state. Separately, Washington and several other states have long had notice laws for health care transactions, such as hospital and physician group deals, that reach smaller deals than HSR does.

Who has to file with the state?

A party must file if it is making an HSR filing and meets either test:

• Principal place of business in the state; or
• In-state sales: it, or a person it controls, had annual net sales in the state of the goods or services involved in the deal of at least 20% of the HSR size-of-transaction threshold.

Because the second test is tied to the federal threshold, it moves when the FTC adjusts HSR thresholds each year. As of November 2026 the HSR threshold is $133.9 million, so 20% is about $26.8 million of in-state sales. Our guide to Hart-Scott-Rodino filing thresholds and fees explains when the federal filing is required in the first place. Deals below the HSR threshold do not trigger these state laws.

The Colorado Attorney General’s premerger notification page states both tests and asks filers to complete an intake form, after which the Department of Law sends instructions for submitting the materials.

What exactly must be filed?

A complete electronic copy of the HSR form. Under Washington’s statute, a filer whose principal place of business is in the state must also include the additional documentary material it submitted with the federal filing. A filer that qualifies only by the sales test provides those documents if the attorney general asks, within seven days of the request. California follows the same split between home-state filers and sales-test filers.

The states must keep the filings confidential. They may share them with the FTC and the Justice Department and with other states that have adopted comparable laws and protections, and Washington’s law requires at least two business days’ notice to the filer before sharing with another state’s attorney general.

What happens after a state receives the filing?

Nothing automatic. The state law adds no waiting period, so a deal can close once the federal waiting period ends. A state attorney general who has concerns can investigate under its existing antitrust powers, issue its own demands for information, join a federal challenge or sue on its own under state or federal antitrust law. For how federal agencies challenge deals, see how the FTC and DOJ block mergers.

Are other states adopting mini-HSR laws?

Bills based on the uniform act were introduced in several other legislatures in 2025 and 2026, among them Hawaii, Indiana and West Virginia. Legislative trackers through early 2026 showed none of them enacted, and the West Virginia bill was reported dead in committee. The Uniform Law Commission tracks enactments of the act, and state legislature websites show the status of each bill.

New York lawmakers have also considered a premerger notification bill of their own, separate from the uniform act. Status changes quickly, so parties planning a filing in 2027 should check each state where they have headquarters or meaningful sales.

Bottom line

For any deal that needs an HSR filing, the extra step is a check of where each party is headquartered and how much it sells in Washington, Colorado and, from 2027, California. Missing the state copy carries daily penalties, while the filing itself costs little or nothing beyond sending the same documents.

FAQ

Does a state mini-HSR filing delay closing?

No. The uniform act adds no waiting period. Closing still depends on the federal HSR waiting period and any other approvals.

Do both buyer and seller have to file with the state?

Each party that makes an HSR filing and meets one of the state tests files its own copy. A seller with no presence in the state may have nothing to file there.

Is the state filing public?

No. The laws require the attorney general to keep the form, the documents and the existence of the proposed merger confidential, with exceptions for sharing with federal agencies and comparable states.

Do these laws apply to deals below the HSR threshold?

No. The uniform act only covers parties that file under HSR. Separate state health care notice laws can reach smaller deals in that sector.