Billionaire entrepreneur Elon Musk has stepped up his legal challenge against OpenAI, the creator of ChatGPT, by filing an expanded lawsuit that now includes OpenAI’s largest backer, Microsoft. The amended complaint, filed Thursday evening in federal court in Oakland, California, alleges that OpenAI and Microsoft are working illegally to monopolize the generative AI market and stifle competition.

The updated lawsuit accuses the two tech giants of violating federal antitrust laws by demanding exclusivity agreements that prevent their rivals from entering the generative AI market. Musk’s filing also argues that Microsoft’s partnership with OpenAI, including its exclusive licensing agreements, essentially acts as a merger without proper regulatory oversight.

“Never before has a company gone from being a tax-exempt charity to a for-profit, market-crippling gorgon of $157 billion – and in just eight years,” the complaint states. Musk is seeking to cancel OpenAI’s licensing deals with Microsoft and force the companies to hand over profits he claims are “ill-gotten.”

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

Musk, who co-founded OpenAI in 2015, has had a contentious relationship with the organization since leaving its board in 2018. He has frequently criticized OpenAI for what he describes as prioritizing profits over ‘to the public good. OpenAI, which gained attention for its ChatGPT platform, is now a key player in the generative AI space, largely fueled by billions of dollars in funding from Microsoft.

Musk’s latest suit also comes as he rises to prominence within US President-elect Donald Trump’s administration. Musk was appointed to a newly created position focused on reducing government waste, following his financial support of Trump’s campaign.

The feud between Musk and OpenAI has grown increasingly heated, with OpenAI alleging in a previous court filing that Musk was using the lawsuit as part of a “braggart campaign to harass OpenAI for his own competitive advantage.”