Billionaire entrepreneur Elon Musk says his artificial intelligence startup, xAI, will sue Apple, alleging the tech giant is engaging in anticompetitive behavior by manipulating App Store rankings to favor rival OpenAI.

“Apple is behaving in a manner that makes it impossible for any AI company besides OpenAI to reach #1 in the App Store, which is an unequivocal antitrust violation. xAI will take immediate legal action,” Musk wrote Monday on X, his social media platform.

Musk did not provide evidence to support his claim, and Apple, OpenAI, and xAI have not yet commented publicly.

App Store rankings currently show OpenAI’s ChatGPT as the top free iPhone app in the U.S., while xAI’s Grok sits in fifth place and Google’s Gemini chatbot ranks 57th. Data from Sensor Tower also shows ChatGPT leading on Google’s Play Store. Apple has an existing partnership with OpenAI to integrate ChatGPT into iPhones, iPads, and Macs.

In an earlier post, Musk directly challenged Apple: “Hey @Apple App Store, why do you refuse to put either X or Grok in your ‘Must Have’ section when X is the #1 news app in the world and Grok is #5 among all apps? Are you playing politics?”

The dispute comes as Apple faces mounting legal and regulatory scrutiny over its App Store practices. In April, a U.S. judge found Apple in violation of a court order requiring greater competition in its app marketplace and referred the company to federal prosecutors for a potential criminal contempt investigation in a case brought by Fortnite creator Epic Games.

That same month, the European Union fined Apple €500 million ($587 million) for allegedly blocking app developers from steering users to cheaper options outside the App Store, in breach of the bloc’s new Digital Markets Act.