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.

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

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.