WASHINGTON, March 3 (Reuters) - U.S. defense contractors, like Lockheed Martin ( LMT ), are expected to follow the Pentagon's order to purge Anthropic's prized AI tools from their supply chains, government contracting and technology attorneys said, even though the Trump administration's ban on their use may fail in court.

The expected exodus from Anthropic was a sign of how quickly firms adjust to the Trump administration's preferences, as they seek to win pieces of its trillion-dollar annual budget, government attorneys said. 

Last Friday, capping off a heated weeks-long dispute with Anthropic over technology guardrails on Claude tools used by the military, President Donald Trump announced a federal agency-wide ban on the company with a six-month phase out period.

Defense Secretary Pete Hegseth went further, promising to designate Anthropic as a supply chain risk to national security and posting: "Effective immediately, no contractor, supplier or partner that does business with the United States military may conduct any commercial activity" with the company.

Anthropic said it would challenge the ban in court.

The move raised immediate legal questions, since none of the authorities that the Trump administration could use to ban Anthropic allow it to also bar its general use by defense contractors, according to lawyers who specialize in technology and contracting laws. 

But the shaky legal basis for the prohibition won't stop companies that depend on the Pentagon from complying with it, the attorneys said, as Lockheed Martin ( LMT ) has pledged to do.

"We will follow the president's and the Department of War's direction," Lockheed Martin ( LMT ) said in a statement, referring to the Department of Defense when asked about its Anthropic use following the moves by the Trump administration. "We expect minimal impacts," the company said, adding that it doesn't depend on any single AI vendor "for any portion of our work."

With huge government contracts at stake, defense contractors would be quick to comply with the Pentagon's ban, lawyers said. 

"Most companies that do significant business with the government are hyper-aware of what the U.S. government wants and they're likely already taking steps to cleanse their supply chains of Anthropic," said Franklin Turner, an attorney who specializes in government contracts.

"Regardless of the legal justification, I think the threat is the point ... it has already done harm, significant harm to the company," he added, referring to Anthropic.

When asked whether they would comply with Trump's order on Anthropic, General Dynamics ( GD ), Raytheon parent RTX, and L3Harris ( LHX ) declined to comment.

The Defense Department did not immediately respond to a request for comment. Anthropic declined to comment but referred Reuters to its Friday statement, in which it asserted that the Pentagon does not have the statutory authority to bar its contractors from using Claude.

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Defense contractors have complied in the past year with Trump's other directives regarding their agreements with the government, according to the news outlet Breaking Defense.

According to the site, they speedily removed references to Diversity, Equity and Inclusion initiatives last year after President Trump signed an executive order mandating all agencies include language in contracts and grant awards requiring any winner to "certify that it does not operate any programs promoting DEI that violate any applicable federal anti-discrimination laws."

Under the authority that the Defense Department is most likely to use, known as the DOD Supply Chain Risk Authority, the agency could bar would-be contractors from using Anthropic in their work for the government, government contracting attorneys said. However, it would not have the power to ban them from using it in their business entirely.

Jason Workmaster, a contract lawyer at Miller Chevalier, described the decision to bar Pentagon contractors from using Anthropic as a "highly aggressive position." 

"If and when challenged, there would be a high likelihood that DOD would be found not to have the authority to do this, unless there are facts that we do not know about," he said.

It is not even clear if the U.S. military has the authority to designate Anthropic as a supply chain risk to bar its own use of the technology.

The Supply Chain Risk Authority has specific requirements for what constitutes a supply chain risk, such as the threat that an adversary may sabotage, introduce unwanted capabilities, or otherwise "subvert" the technology in order to "surveil, deny or disrupt" its use.

Meanwhile the Federal Acquisition Supply Chain Security Act (FASCSA), which creates a similar authority, requires the agency to follow several steps prior to a ban, such as giving the business the opportunity to respond and notifying Congress, among others.

The U.S. government so far hasn't shown publicly that it satisfied the requirements, said Alan Rozenshtein, a University of Minnesota law professor who specializes in technology regulation.

"Capitalism and free markets rely on the rule of law," he said. "This is the opposite of that."

The Trump administration used FASCSA last year to bar intelligence agencies from buying products from Acronis AG, a Swiss cybersecurity and data protection company.