The software giant has filed an amicus brief, urging a federal judge in San Francisco to temporarily block the Pentagon’s designation of Anthropic as a supply chain risk, News.Az reports, citing foreign media.
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Microsoft is also a major Defense Department contractor that integrates Anthropic’s technology into some of its offerings, and hence, has argued that the designation, typically reserved for foreign adversaries, oversteps in response to a contract dispute. “The use of a supply chain risk designation to address a contract dispute may bring severe economic effects that are not in the public interest,” Microsoft stated in its filing.
Microsoft backs Anthropic in lawsuit against Pentagon
The company warned that without a temporary restraining order, Microsoft and other tech providers would face immediate disruptions, needing to “alter existing product and contract configurations” for military systems.
Microsoft also endorsed Anthropic’s ethical safeguards, noting alignment with broader American values. “Microsoft also believes that American AI should not be used to conduct domestic mass surveillance or start a war without human control. This position is consistent with the law and broadly supported by American society, as the government acknowledges.”
The move comes amid Anthropic’s lawsuit against the Trump administration, challenging what the company calls an “unprecedented and unlawful” label, which effectively bans its Claude AI models from US military contracts. The ban also forces government contractors to cease related usage.
The dispute escalated after failed negotiations between the Pentagon and Anthropic over unrestricted military access to Claude. Anthropic refused to remove restrictions on applications like fully autonomous weapons or mass domestic surveillance, insisting that its “constitution”-based safety principles be reserved. In response, Defense Secretary Pete Hegseth designated Anthropic a supply chain risk last week, and President Donald Trump directed all federal agencies to stop using Claude.
Anthropic filed its lawsuit on March 9 in US District Court in San Francisco, seeking to challenge the label and related bans. The company argues the actions violate due process and free speech, threatening hundreds of millions, and potentially billions, in government-related business.
Microsoft’s intervention is joined by a group of retired military leaders and other tech firms, including reports of Google, Amazon, Apple, and OpenAI signing supportive briefs. This coalition highlights concerns over using supply chain risk tools against domestic US companies and the potential negative effect on AI innovation for defence purposes.
The Pentagon has declined to comment on ongoing litigation.
