Microsoft has filed an amicus brief in support of Anthropic's lawsuit against the Department of Defense.

The suit calls for the court to issue a temporary restraining order against the Pentagon's designation of the company as a supply chain risk, ahead of a longer court ruling on the legality of the decision.

The designation came after Anthropic refused to change its terms of service, which prohibit mass surveillance and fully autonomous weapons. Anthropic's CEO, Dario Amodei, also said in internal comments - which he has since walked back - that the company was punished for not donating to Trump or giving "dictator-like praise."

The Department of Defense (DoD) - now stylized as Department of War - has six months to remove Anthropic products from its systems, while contractors have been told to immediately remove Claude and other products. In its lawsuit, Anthropic said this could undermine investor confidence and, ultimately, doom the company.

Anthropic investor Microsoft backed the company's request for a temporary restraining order. Anthropic is set to spend $30bn on Azure cloud, while its services are available on Azure.

"As an Anthropic partner, Microsoft is directly impacted by DoW’s designation that Anthropic presents a supply chain risk to national security," the company said in its brief.

"Microsoft believes the Court should temporarily enjoin implementation of the Determination for all existing contracts and their ongoing use of Anthropic products, including with and through Microsoft products."

The company said that a temporary restraining order would enable a more orderly transition and avoid disrupting the American military’s ongoing use of advanced AI.

Removing Anthropic would cost contractors "significant resources" and risk delaying DoD contracts, impacting any war efforts. Longer term, the determination would mean that working with Anthropic "would pose new risks and attendant costs affecting public sector and commercial operations."

Alongside Microsoft's brief, nearly 40 employees from OpenAI and Google, including Google DeepMind chief scientist Jeff Dean, filed their own brief in support of Anthropic.

“If allowed to proceed, this effort to punish one of the leading US AI companies will undoubtedly have consequences for the United States’ industrial and scientific competitiveness in the field of artificial intelligence and beyond,” the employees said.

"It will chill open deliberation in our field about the risks and benefits of today’s AI systems."