Microsoft Backs Anthropic’s Bid to Block the Pentagon’s Supply-Chain Risk Label

Microsoft warned that U.S. warfighters could be hampered if the Pentagon’s designation of Anthropic is implemented.

A man looks at his phone in front of the Microsoft logo during the 2025 Mobile World Congress in Barcelona on March 3, 2025. Albert Gea/Reuters

Microsoft on March 10 filed an amicus brief backing Anthropic’s lawsuit against the Department of War, seeking a court order to temporarily stop the Pentagon from labeling Anthropic as a supply-chain risk.

Anthropic filed the suit on March 9 after the Pentagon designated it a supply chain risk to national security, a label that would hinder the Pentagon and its contractors from using Anthropic’s artificial intelligence technology in their work for the U.S. military.

The designation stemmed from Anthropic’s rejection of the Pentagon’s request for unrestricted access to its Claude models over concerns that the technology could be used for mass domestic surveillance or fully autonomous weapons. The Pentagon has denied that it planned to use Claude for such purposes.

In its amicus brief filed March 10, Microsoft said it was directly affected by the Pentagon’s designation of Anthropic because it uses Anthropic’s technologies in products made available to the Pentagon.

The tech giant said that a temporary block on the designation would “enable a more orderly transition and avoid disrupting the American military’s ongoing use of advanced AI.”

Microsoft warned that U.S. warfighters could be hampered “at a critical point in time” if companies are required to immediately alter existing product and contract configurations used by the Pentagon.

It also warned that putting the Pentagon’s designation of Anthropic into immediate effect will have “broad negative ramifications for the entire technology sector and the American business community.”

Microsoft said the Pentagon gave itself a six-month period to transition services away from Anthropic’s technologies but did not provide the same transition timeline for contractors that use Anthropic products.

“Should this action proceed without the entry of a temporary restraining order, Microsoft and other government contractors with expertise in developing solutions to support U.S. government missions will be forced to account for a new risk in their business planning,” it stated.

“Should companies choose to forgo the opportunity to work with the U.S. government due to the attendant risks, the U.S. government, its missions, and the people it serves would lose access to state-of-the-art technological solutions,” Microsoft said.

The Pentagon said it does not comment on ongoing litigation.

Anthropic alleged in its lawsuit that the federal government designated the company in retaliation for its viewpoint protected under the First Amendment.

Secretary of War Pete Hegseth on Feb. 27 accused Anthropic of trying to dictate military operations by denying the Pentagon permission to use its Claude models for all lawful purposes.

“Their true objective is unmistakable: to seize veto power over the operational decisions of the United States military. That is unacceptable,” Hegseth said in a post on X.

The Pentagon used the Claude AI system for mission-critical functions, including intelligence analysis, modeling and simulation, operational planning, and cyber operations.