(Refiles to correct media story identifier to from USA-PENTAGON/USA)

By Jack Queen

NEW YORK, March 17 (Reuters) - The Trump administration said in a Tuesday court filing that the Pentagon's blacklisting of Anthropic was justified and lawful, opposing the artificial intelligence lab's high-stakes lawsuit challenging the decision. 

Defense Secretary Pete Hegseth designated Anthropic, the maker of popular AI assistant Claude, a national security supply chain risk on March 3 after the company refused to remove guardrails against its technology being used for autonomous weapons or domestic surveillance.

The Trump administration's filing says Anthropic is unlikely to succeed on its claims that the U.S. action violated speech protections under the U.S. Constitution's First Amendment, asserting the dispute stems from contract negotiations and national security concerns, not retaliation.

"It was only when Anthropic refused to release the restrictions on the use of its products - which refusal is conduct, not protected speech - that the President directed all federal agencies to terminate their business relationships with Anthropic," the administration's legal filing said. The filing, from the U.S. Justice Department, said "no one has purported to restrict Anthropic's expressive activity."

Anthropic's lawsuit in California federal court asks a judge to block the Pentagon's decision while the case plays out. Some legal experts say the company appears to have a strong case that the government overreached. 

President Donald Trump backed Hegseth's move, which excludes Anthropic from a limited set of military contracts but could damage the company's reputation and cause billions of dollars in losses this year, according to its executives. 

The designation came after months of negotiations between the Pentagon and Anthropic reached an impasse, prompting Trump and Hegseth to denounce the company and accuse it of endangering American lives with its usage restrictions. 

Anthropic has disputed those claims and said AI is not yet safe enough to be used in autonomous weapons. The company said it opposes domestic surveillance as a matter of principle. 

In its March 9 lawsuit, Anthropic said the "unprecedented and unlawful" designation violated its free speech and due process rights, while running afoul of a law requiring federal agencies to follow specific procedures when making decisions. 

The Pentagon separately designated Anthropic a supply chain risk under a different law that could expand the order to the entire government. 

Anthropic is challenging that move in a second lawsuit in a Washington, D.C. appeals court.