Microsoft Joins the Fight for Anthropic as Pentagon’s AI Ethics War Expands Into Congress and the Courts

Microsoft has joined the fight for Anthropic on multiple fronts as the AI company’s battle with the Pentagon over AI ethics simultaneously expands into Congress and the federal courts. The company filed an amicus brief in a San Francisco federal court calling for a temporary restraining order against the Pentagon’s supply-chain risk designation. Amazon, Google, Apple, and OpenAI have also backed Anthropic through a separate court filing, while congressional Democrats have launched parallel investigations into related AI governance concerns.
Anthropic’s legal challenge stems from the Pentagon’s unprecedented decision to label it a supply-chain risk after the company refused to allow its Claude AI to be used for mass surveillance of US citizens or to control autonomous lethal weapons during a $200 million contract negotiation. Defense Secretary Pete Hegseth formalized the designation following the breakdown of talks, and Anthropic’s government contracts began to be cancelled. The company filed two simultaneous lawsuits in California and Washington DC.
Microsoft’s participation in the fight reflects 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 agreements with defense, intelligence, and civilian agencies worth several billion dollars more. Microsoft publicly argued that the government and the technology sector needed to cooperate to ensure advanced AI serves national security without crossing ethical lines related to surveillance or autonomous warfare.
Anthropic’s court filings argued that the supply-chain risk designation was an unconstitutional act of retaliation for the company’s publicly stated AI safety positions. 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 possibility of renewed negotiations.
Congressional Democrats have separately written to the Pentagon demanding information about whether AI was involved in a strike in Iran that reportedly killed over 175 civilians at a school. Their inquiries ask specifically about AI targeting tools and human oversight processes. The convergence of these congressional investigations with Anthropic’s lawsuits and Microsoft’s legal intervention is creating an unprecedented multi-front battle over AI governance that spans the judiciary, the legislature, and the executive branch.