The Trump administration acted illegally when it labeled the artificial intelligence start-up Anthropic a security risk and barred the company from working with the U.S. government, a federal judge ruled on Thursday.

Judge Rita Lin of the U.S. District Court in the Northern District of California wrote in her 59-page ruling that the government had unlawfully retaliated against Anthropic “for constitutionally protected expressive activities” after the A.I. company spoke out about how its technology should be used.

“The empty invocation of national security is not a blank check to punish and retaliate against government critics,” she wrote.

In a statement, Anthropic said: “We welcome the court’s ruling that this supply chain risk designation was unlawful. We remain focused on working productively with the government to harness A.I. for our national security so all Americans benefit from this technology.”

The Trump administration did not immediately respond to a request for comment.

The ruling caps the first of two lawsuits that Anthropic filed on March 9 in response to the Trump administration’s action. The second lawsuit, filed in the U.S. Court of Appeals for the District of Columbia Circuit, is ongoing. The Trump administration could appeal Judge Lin’s ruling or wait for a decision in the second lawsuit before taking action, a person with knowledge of the matter said.

The California ruling is the latest chapter in the fight between the Trump administration and Anthropic, which is heading toward what may be the biggest-ever initial public offering.