Microsoft has mobilized top legal support for Anthropic by filing an amicus brief in a San Francisco federal court as the Pentagon’s supply-chain risk designation faces its first serious courtroom scrutiny. The brief called for a temporary restraining order and argued that the designation poses an immediate threat to the defense and commercial technology supply chains that depend on Anthropic’s AI. Amazon, Google, Apple, and OpenAI have also backed Anthropic through a joint court filing, making this a comprehensive industry response to the government’s action.
Anthropic’s legal troubles began when the company refused to enter a $200 million contract with the Pentagon without protections against using its Claude AI for mass domestic surveillance or autonomous lethal weapons. Defense Secretary Pete Hegseth responded by labeling the company a supply-chain risk, leading to the cancellation of Anthropic’s government contracts. Anthropic filed two simultaneous lawsuits in California and Washington DC arguing the designation was unconstitutional and without precedent.
Microsoft’s brief is anchored in its direct use of Anthropic’s AI in 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 agreements with defense, intelligence, and civilian agencies. Microsoft publicly argued that the government and the technology sector must cooperate to ensure advanced AI serves national security without crossing ethical lines related to surveillance or unauthorized military action.
Anthropic’s lawsuits argued that the supply-chain risk designation, normally reserved for firms linked to foreign adversaries, was being misused as a political weapon against a US company for its publicly expressed views on AI safety. The company’s court filings disclosed that it does not currently believe Claude is safe or reliable enough for lethal autonomous operations, which it said was the genuine and urgent basis for its contract demands. The Pentagon’s technology chief publicly foreclosed any possibility of renegotiation.
Congressional Democrats have separately written to the Pentagon asking whether AI was used in a strike in Iran that reportedly killed over 175 civilians at a school, demanding answers about AI targeting tools and human oversight. Their inquiries are adding legislative urgency to what is already a significant legal confrontation. Together, the congressional inquiries, Microsoft’s court mobilization, and the industry coalition are creating an unprecedented moment of scrutiny for the Pentagon’s approach to AI in warfare.