March 12, 2026 Microsoft has asked a U.S. federal court to temporarily block the Pentagon from enforcing a decision that labels AI company Anthropic a “supply-chain risk,” a designation that prevents defence contractors from using its technology. The filing supports Anthropic’s request for a temporary restraining order that would allow existing U.S. military contracts using its AI models to continue while the lawsuit proceeds.
Microsoft’s position was submitted as a proposed amicus brief in U.S. District Court in San Francisco.
The dispute began after the U.S. Department of Defense last week designated Anthropic as a supply-chain risk, a classification historically applied to foreign adversaries. The ruling requires contractors working with the Pentagon to certify that they do not use Anthropic’s AI models.
Anthropic filed a lawsuit Monday against the U.S. government, arguing the designation is “unprecedented and unlawful” and threatens hundreds of millions of dollars in contracts. The conflict follows failed negotiations between the company and the Pentagon over how Anthropic’s AI models could be used in military settings.
According to reports, Anthropic sought assurances that its systems would not be used for domestic mass surveillance or fully autonomous weapons. The Defense Department reportedly wanted broader access for lawful military purposes, and the talks collapsed.
Microsoft warned in its filing that immediate enforcement of the designation could disrupt existing technology deployments used by the U.S. military.
Without a temporary order pausing the decision, the company said technology providers would have to quickly modify product configurations and contracts supporting the Pentagon. Microsoft said that disruption “could potentially hamper U.S. warfighters at a critical point in time.”
Support for Anthropic has also emerged from within the AI research community. More than 30 employees from OpenAI and Google, including Google DeepMind chief scientist Jeff Dean, submitted their own amicus brief expressing concern that the designation could affect innovation in the AI sector.
Anthropic, founded in 2021 by former OpenAI executives, has rapidly grown into one of the most prominent AI startups in the United States. The company recently reached a reported valuation of $380 billion and has attracted major backing from technology companies including Microsoft.
