Microsoft has fired a legal warning shot at the Pentagon by filing an amicus brief in a San Francisco federal court that challenges the Defense Department’s unprecedented decision to blacklist Anthropic as a supply-chain risk. The brief called for a temporary restraining order and warned of serious harm to technology supply chains if the designation is allowed to stand. Amazon, Google, Apple, and OpenAI have also signed on to a supporting brief, making this one of the most broadly backed legal challenges to a government action in recent US history.
The Pentagon’s designation of Anthropic as a supply-chain risk followed the collapse of a $200 million contract in which the company refused to allow its Claude AI to be used for mass surveillance of US citizens or to power autonomous lethal weapons. Defense Secretary Pete Hegseth applied the designation, which had never before been used against a domestic American company, and Anthropic’s government contracts began to be cancelled. Anthropic filed two simultaneous lawsuits in California and Washington DC.
Microsoft’s warning shot carries significant credibility given its status as one of the Pentagon’s most deeply embedded technology partners. The company uses Anthropic’s AI in military systems it provides to the federal government and is a partner in the $9 billion Joint Warfighting Cloud Capability contract. Microsoft publicly called for a collaborative approach in which the government and technology industry work together to ensure advanced AI serves national security without being misused for surveillance or unauthorized warfare.
Anthropic’s court filings argued that the supply-chain risk designation violated its First Amendment rights by punishing the company for publicly advocating responsible AI development. The company disclosed that it does not currently believe Claude is 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 prospect of renewed negotiations.
Congressional Democrats have separately written to the Pentagon demanding information about whether AI was used in a strike in Iran that reportedly killed over 175 civilians at a school. Their formal letters ask about AI targeting systems and human oversight processes. These legislative inquiries, combined with Microsoft’s legal warning shot and the industry’s coordinated court filings, are creating a moment of extraordinary pressure on the Pentagon over its approach to AI in warfare.
