Elon Musk has expanded his lawsuit against the ChatGPT maker OpenAI, adding federal antitrust and other claims and adding OpenAI’s largest financial backer, Microsoft, as a defendant.

Musk’s amended lawsuit, filed on Thursday night in federal court in Oakland, California, said Microsoft and OpenAI illegally sought to monopolize the market for generative artificial intelligence and sideline competitors.

Like Musk’s original August complaint, it accused OpenAI and its chief executive, Samuel Altman, of violating contract provisions by putting profits ahead of the public good in the push to advance AI.

“Never before has a corporation gone from tax-exempt charity to a $157bn for-profit, market-paralyzing gorgon – and in just eight years,” the complaint said. It seeks to void OpenAI’s license with Microsoft and force them to divest “ill-gotten” gains.

OpenAI in a statement said the latest lawsuit “is even more baseless and overreaching than the previous ones”. Microsoft declined to comment.

“Microsoft’s anticompetitive practices have escalated,” Musk’s attorney Marc Toberoff said in a statement. “Sunlight is the best disinfectant.”

Musk has a long-simmering opposition to OpenAI, a startup he co-founded and that has since become the face of generative AI through billions of dollars in funding from Microsoft.

Musk has gained new prominence as a key force in Donald Trump’s incoming administration. Trump named Musk to a new role designed to cut government waste, after he donated millions of dollars to Trump’s Republican campaign.

The expanded lawsuit said OpenAI and Microsoft violated antitrust law by conditioning investment opportunities on agreements not to deal with the companies’ rivals. It said the companies’ exclusive licensing agreement amounted to a merger lacking regulatory approvals.

In a court filing last month, OpenAI accused Musk of pursuing the lawsuit as part of an “increasingly blusterous campaign to harass OpenAI for his own competitive advantage”.