Microsoft has amplified Anthropic’s legal voice in a battle that has gone national, filing an amicus brief in a San Francisco federal court in support of the AI company’s challenge to the Pentagon’s supply-chain risk designation. The brief called for a temporary restraining order and warned of the serious harm the designation could cause to defense and commercial technology supply chains. Amazon, Google, Apple, and OpenAI have similarly backed Anthropic through a joint court filing.
Anthropic’s legal challenge was triggered by the Pentagon’s decision to label it a supply-chain risk after the company refused to allow its Claude AI to be used for mass surveillance or autonomous lethal weapons as part of a $200 million contract negotiation. Defense Secretary Pete Hegseth formalized the designation following the collapse of talks, triggering the cancellation of Anthropic’s government contracts. The company filed two simultaneous lawsuits in California and Washington DC.
Microsoft’s participation in the case is grounded in its direct integration of Anthropic’s technology into military systems it provides to the federal government and its partnership in the Pentagon’s $9 billion cloud computing contract. The company also holds additional federal agreements spanning defense, intelligence, and civilian agencies. Microsoft publicly argued that responsible AI governance and effective national defense were goals that the government and industry must pursue in collaboration.
Anthropic’s lawsuits argued that the supply-chain risk designation was an unconstitutional act of retaliation for the company’s publicly held views on AI safety, violating its First Amendment rights. The company disclosed that it does not believe Claude is currently safe or reliable enough for lethal autonomous operations, which it said was the genuine basis for its contract demands. The Pentagon’s technology chief publicly ruled out any possibility of renewed negotiations.
House Democrats have separately written to the Pentagon asking whether AI was used in a strike in Iran that reportedly killed more than 175 civilians at a school, demanding answers about AI targeting tools and human oversight. Their inquiries are running parallel to Anthropic’s lawsuits and adding legislative urgency to the confrontation. Together, these developments are forcing an unprecedented public debate about the accountability and governance of AI in American military operations.