Elon Musk claims that Apple has threatened to “withhold” Twitter from the iOS App Store for unknown reasons. The news follows a tweet where Musk said Apple had “mostly stopped advertising” on the platform and a poll asking whether Apple should “publish all censorship actions it has taken that affect its customers.” Apple did not immediately comment on Musk’s claim.

The news follows much more subtle signs of mounting tension between Apple and Musk-owned Twitter. Musk has criticized Apple’s App Store fee for in-app purchases, dubbing it a “hidden 30% tax” on the internet. And Apple App Store boss Phil Schiller deleted his Twitter account following Musk’s takeover, shortly after Donald Trump’s account was reinstated.

In a November 15th interview with CBS News, Apple CEO Tim Cook said that “they say that they are going to continue to moderate. I’m counting on them to continue to do that.” Musk, however, has pledged to loosen Twitter’s moderation guidelines and floated the idea of a mass unbanning of suspended accounts.

Twitter has long tested the boundaries of Apple’s App Store moderation — which has successfully pushed Discord, Tumblr, and other services to either hide potentially offensive content (typically adult content) or ban it altogether. Twitter remains one of the only large platforms to still allow adult content on its app, and a recent editorial by former Twitter executive Yoel Roth revealed that it’s sparred periodically with Apple over content like racial slurs and the hashtag #boobs.

If Musk’s statement is accurate, “withhold” could mean temporarily rejecting an update to the Twitter app or could involve a more serious threat to boot Twitter from the iOS App Store — a devastating potential outcome for Twitter.