A hot potato: Apple has clashed with plenty of companies in the past, and now a group of them, including Epic Games and Spotify, have formed a nonprofit group to challenge Cupertino's App Store practices. The Coalition for App Fairness says it has been founded to "advocate for freedom of choice and fair competition across the app ecosystem."

Virtually all 13 founding app developers have butted heads with Apple. Epic, of course, is currently suing Apple over antitrust claims after Fortnite was removed from the App Store following the introduction of Epic's own in-app payment platform.

Spotify launched a complaint against Apple last year, calling the 30 percent cut it takes from developers unfair. The music streaming giant said that Apple acts as "the stadium owner, referee, and player, and tilts the playing field in favor of its own services."

The group has set out 10 "App Store Principles" in its demands. These include no developer being made to use an app store exclusively, not being blocked from a platform based on a company's business practices, and not having to pay unfair, unreasonable or discriminatory fees.

"As enforcers, regulators, and legislators around the world investigate Apple for its anti-competitive behavior, The Coalition for App Fairness will be the voice of app and game developers in the effort to protect consumer choice and create a level playing field for all," said Horacio Gutierrez, head of global affairs at Spotify.

The website notes the disparity between the 30 percent fee apple takes and the maximum 5 percent upper limit fees charged by other payment providers for purchases. Apple, whose market cap recently passed the $2 trillion milestone, made over $50 billion in store tax revenue last year.