Reports surfaced yesterday that Spotify's counsel Horacio Gutierrez sent a letter to Apple last week to let the company know what it thought about a pending app update being held up. The streaming service is taking issue with the App Store's 30 percent fee for use of its billing system for subscriptions that applies to all developers. In other words, if users sign up through Spotify's iOS app, they're charged $13 a month instead of the usual $10 to cover the fee. Sewell explained that Apple treats all app devs the same across games, e-books and both video and music streaming, and more specifically that those terms didn't change when Apple Music launched and Spotify became a direct competitor.

"Ironically, it is now Spotify that wants things to be different by asking for preferential treatment from Apple," Sewell said. He went on to reiterate that nothing about how the system is set up violates antitrust laws like Gutierrez argued in his own letter last week. What's more, the Spotify app that's currently available in the App Store actually violates the company's guidelines.

"I would be happy to facilitate an expeditious review and approval of your app as soon as you provide us with something that is compliant with the App Store's rules," Sewell said.

Neither Apple nor Spotify responded to Engadget's request for comments on the matter.