Elon Musk lashed out against Apple Inc.’s app store practices late on Monday, accusing the iPhone maker of favoring OpenAI.

The billionaire founder of xAI Holdings, which now houses the Grok artificial intelligence team and X social network, said Apple makes it impossible for anyone other than OpenAI to reach the top of the App Store charts, a sought-after global spotlight for app developers.

In a pinned post on his X account, Musk asked if Apple is “playing politics” by not highlighting his products.

READ MORE: Musk warns to ban Apple devices if OpenAI is integrated at operating system level

His comments mark the biggest fight that Musk, 54, has picked since his confrontation with US President Donald Trump in June, when each man posted disparaging remarks about the other on his own social network.

Apple and OpenAI representatives didn’t immediately respond to requests for comment.

Musk added that xAI will take legal action against what he deemed an antitrust violation.

ALSO READ: Musk clashes with Altman over $500b 'Stargate' deal to build data centers for OpenAI

Apple and OpenAI — whose ChatGPT is the most-downloaded free iPhone app in the US, ahead of Grok at No. 5 — have a partnership around AI built into the latest iPhones.

Musk a long-running feud with OpenAI Chief Executive Officer Sam Altman, which dates back to disagreements that led to their split after the two founded OpenAI together.