Microsoft Calls on Federal Court to Stop Pentagon’s AI Blacklist as Anthropic’s Lawsuit Gains Momentum

Microsoft has called on a federal court in San Francisco to halt the effects of the Pentagon’s controversial blacklisting of Anthropic, filing an amicus brief that argues the designation poses an immediate and serious threat to defense and commercial technology networks. The brief requested a temporary restraining order and was accompanied by a separate filing from Amazon, Google, Apple, and OpenAI. The tech industry’s collective response to the Pentagon’s action is growing in momentum and legal significance.
Anthropic was designated a supply-chain risk by the Pentagon after it refused to allow its Claude AI to be deployed for mass surveillance or autonomous lethal weapons as part of a $200 million contract negotiation. Defense Secretary Pete Hegseth formalized the designation following the breakdown of talks, and the company’s existing government contracts began to be cancelled. Anthropic filed two separate lawsuits challenging the designation in California and Washington DC courts on the same day.
Microsoft’s brief is particularly significant because the company integrates Anthropic’s AI into systems it provides to the US military and participates in the Pentagon’s $9 billion Joint Warfighting Cloud Capability contract. Additional federal agreements spanning defense, intelligence, and civilian agencies further deepen Microsoft’s stake in this dispute. Microsoft publicly argued that ensuring access to top AI technology and preventing its misuse were goals the government and tech sector needed to pursue together.
Anthropic’s legal filings argued that the supply-chain risk designation was an unconstitutional act of retaliation against the company for publicly advocating responsible AI development. The company stated that it does not currently believe Claude is safe or reliable enough for lethal autonomous operations, which it said was the genuine reason for the restrictions it sought in the contract. Anthropic pointed out that the designation had never before been applied to a US company and accused the Pentagon of using it as a political weapon.
Congressional Democrats are simultaneously pressing the Pentagon for information about whether AI was involved in a strike in Iran that reportedly killed more than 175 civilians at an elementary school. Their inquiries ask specifically about AI’s role in targeting and whether human review processes were followed. The combination of Anthropic’s growing legal momentum, Microsoft’s court intervention, and congressional pressure is creating a pivotal moment for AI governance in the United States.