Microsoft is putting its enormous leverage as one of the Pentagon’s most important technology partners behind Anthropic’s historic lawsuit challenging the Defense Department’s unprecedented supply-chain risk designation. The company filed an amicus brief in a San Francisco federal court calling for a temporary restraining order, warning that the designation could cause immediate and serious harm to defense and commercial technology supply chains. Amazon, Google, Apple, and OpenAI have also thrown their support behind Anthropic through coordinated legal filings.
The Pentagon’s designation was triggered by the breakdown of a $200 million contract negotiation in which Anthropic refused to allow its AI to be used for mass surveillance of US citizens or to power autonomous lethal weapons. Defense Secretary Pete Hegseth labeled the company a supply-chain risk, and the company’s existing government contracts began to be cancelled. Anthropic filed two lawsuits simultaneously in California and Washington DC, arguing the designation violated its constitutional rights and was unprecedented for a US company.
Microsoft’s brief is grounded in its direct use of Anthropic’s AI in federal military systems and its partnership in the Pentagon’s $9 billion cloud computing contract. The company also holds additional federal agreements worth billions of dollars spanning defense, intelligence, and civilian agencies. Microsoft publicly called for government and industry to work collaboratively to ensure that AI serves national security goals without enabling surveillance or unauthorized warfare.
Anthropic’s court filings argued that the supply-chain risk designation was an act of unconstitutional retaliation for the company’s publicly stated AI safety positions. The company disclosed that it does not believe Claude is currently safe or reliable enough for lethal autonomous decision-making, which it said was the genuine and urgent basis for the restrictions it sought in the contract. The Pentagon’s technology chief publicly ruled out any possibility of renewed negotiations.
Congressional investigators are adding pressure from another direction, demanding answers from the Pentagon about whether AI was used in a strike in Iran that reportedly killed more than 175 civilians at a school. Lawmakers are asking whether AI targeting systems were involved and whether human review processes were adequate. The combined force of Microsoft’s legal intervention, the industry coalition, and congressional scrutiny is creating a pivotal and potentially historic moment for AI governance in the United States.