Elon Musk is threatening to take legal action against Microsoft over claims that the company “trained illegally using Twitter data.” The billionaire’s statement came in response to a tweet noting that Microsoft’s advertising platform announced it would stop supporting Twitter, reportedly due to Twitter’s changes requiring payment to access its API.

Musk’s threat is vague but appears to be over OpenAI using Twitter data to train the large language model behind products like ChatGPT. OpenAI, obviously, is not Microsoft, but it did recently receive a significant investment from the company, which is building AI into tools like Bing, Edge, and Microsoft 365.

It’s unclear whether Musk will actually sue Microsoft at this point, as he has threatened legal action that never happened in the past, including against the creator of the @ElonJet Twitter account.

Microsoft declined to comment. Twitter’s press email replied with a poop emoji when reached for comment.

In a message on the top of a support page for Microsoft’s advertising platform, the company says it will “no longer support Twitter” starting on April 25th, 2023, which means companies can no longer use Microsoft’s platform to manage their tweets or engagement. This also coincides with Twitter’s timeline to put its API (application programming interface) behind a paywall.

Under Twitter’s new pricing arrangement, large companies like Microsoft could have to pay as much as $42,000 per month to gain access to Twitter’s API. The new pricing system has already led some smaller developers to abandon the platform, such as Tweetbot maker Tapbots.

Update April 19th, 8:05PM ET: Microsoft declined to comment.