Elon Musk says that Apple has threatened to withhold Twitter from its App Store for unknown reasons. The billionaire CEO said in a tweet that Apple made the threat, “but won’t tell us why.”

This comes after 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.”

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This shows much stronger signs of mounting tension between Apple and Twitter. Musk has criticized Apple’s App Store fee for in-app purchases, calling it a “hidden 30% tax” on the internet. Apple App Store head Phil Schiller deleted his Twitter account following Musk’s takeover, shortly after Donald Trump’s account was unbanned.

In an interview with CBS News on November 15, 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.”

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However, Musk has pledged to loosen Twitter’s moderation guidelines and shared the idea of mass unbanning of suspended accounts. Twitter has long tested the boundaries of Apple’s App Store moderation, which has successfully prompted Tumblr, Discord, and other services to either hide or ban potentially offensive content (typically adult content). Twitter remains only one of the big platforms to still allow adult content on its platform. The latest editorial by former Twitter executive Yoel Roth showed that it’s sparred periodically with Apple over content like racial slurs and hashtags.

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The social media company announced it would relaunch its paid verification check service next week after delays over impersonation concerns. Musk indicated the platform would issue gold checks for companies, grey checks for government accounts, and blue checks for individual accounts.

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The move had raised controversy for introducing an $8-per-month subscription service that includes a blue tick on accounts after a series of users quickly leveraged it to prominent companies and public figures.