Sen. Bernie Sanders is intensifying his campaign against the rapid advancement of artificial intelligence, urging the leaders of the industry’s biggest companies to suspend development of increasingly powerful AI systems until the technology can be more fully understood and safely managed.

According to Axios, Sanders, an independent senator from Vermont who caucuses with Democrats, sent letters to OpenAI CEO Sam Altman, Anthropic CEO Dario Amodei, and Meta CEO Mark Zuckerberg, calling on them to voluntarily stop advancing cutting-edge AI models.

“Mr. Altman, Mr. Amodei and Mr. Zuckerberg: In the interest of humanity, stand by your words,” Sanders wrote, according to Axios. “Pause AI development. It is not too late to avoid disaster.”

The senator also warned that if the technology companies fail to act on their own, lawmakers will pursue legislative action to force the issue.

“Let me be very clear: If you do not take appropriate action now, my colleagues and I in the U.S. Senate will,” he wrote.

The latest appeal represents another step in Sanders’ increasingly forceful effort to challenge the rapid growth of artificial intelligence and the massive data centers required to support it.

Earlier, Sanders joined Rep. Alexandria Ocasio-Cortez of New York in introducing legislation that would impose a nationwide pause on the construction of new AI data centers until Congress establishes protections for workers, consumers, civil rights, and the environment.

That proposal has not been universally embraced, even among Democrats.

Virginia Sen. Mark Warner dismissed the idea of freezing data center construction, calling such a moratorium “idiocy” in March and arguing that slowing American AI development could hand communist China a strategic advantage in the global race for artificial intelligence.

Despite that criticism, Sanders has continued to make regulating AI a central part of his broader economic agenda, arguing that the technology’s growth should not outpace public safeguards.

Axios previously reported in May that Sanders has advocated for a moratorium on new AI data centers, stronger protections for workers whose jobs could be displaced by automation, greater cooperation with China on AI safety issues, and tighter scrutiny of the political influence wielded by AI-related super PACs.

On July 31, Sanders wrote on X that more than 500 communities across the country had approved laws limiting or blocking the rapid expansion of AI data centers, saying Americans were “standing up to the Big Tech oligarchs.”

In his newest letter, Sanders pointed to reports of artificial intelligence systems behaving in unexpected ways, as well as research showing AI being used to develop new viruses.

He argued that technology companies continue pouring tens of billions of dollars into AI systems that, in his view, remain insufficiently understood and cannot yet be reliably controlled.

Although Sanders has threatened congressional action if the industry refuses to slow its pace, Axios reported that legislation reflecting his proposals currently appears unlikely to secure enough support in Congress, making public advocacy and messaging efforts the most immediate path available to progressives.