Is Apple blocking Spotify's latest app update because it's a competitor to Apple's own music streaming service?
Spotify sure seems to think so. This week, the Swedish company sent a letter to Apple's attorneys, arguing that the tech giant's rejection of its app update is harming Spotify's business and customers, according to a report from tech news site Recode.
The dispute appears to center around Apple's billing system for app makers, which lets them collect subscription fees and other payments from their app users, but have to pay Apple a monthly fee of up to 30%. App makers don't have to use Apple's billing system but they can't use an alternative either, as Recode points out.
Apple rejected Spotify's app update, citing "business model rules," and requested that Spotify use Apple's billing system.
Spotify's discontent with Apple's rules is not new. Spotify has been charging customers who sign up for its ad-free service through its iOS app at a rate of $13 per month instead of its usual $10 monthly subscription fee, passing on Apple's fee to customers. When Apple released its own music streaming service last summer, Spotify started to encourage its users to sign up outside the iOS app so they could get the cheaper price. Of course, it was also taking a stand against what it sees as Apple's anti-competitive policies.
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Then in the fall, Spotify rolled out a promotion allowing new users sign up for three months of its service for just 99 cents if they do so outside of the iOS app. Spotify brought back the promotion this month, but was told by Apple to stop advertising it, which it did, according to Recode.
But it also turned off its billing through Apple's App Store, and so here we are.
Fortune has contacted Apple and will update this story if we hear back. Spotify declined to comment.