Epic Games Inc's "Fortnite: Battle Royale" video game is displayed for a photograph on an Apple Inc iPhone in Washington on May 10, 2018. (ANDREW HARRER / BLOOMBERG)

Epic Games Inc added a new front to its legal battle against Apple Inc by filing a complaint with European Union regulators over the iPhone maker’s App Store rules.

The maker of Fortnite said that it was asking the EU to step in after facing retaliation for trying to sidestep Apple’s requirement for programs downloaded from the App Store to use the tech giant’s own payment system and pay a commission of as much as 30 percent.

ALSO READ: EU opens two Apple antitrust probes

Epic Games is already suing Apple in the US and Australia and also filed complaints about Apple and Google app stores at the UK’s antitrust tribunal

“Apple should not have any right to block or tax a transaction through other payment services,” Epic Games Chief Executive Officer Tim Sweeney told reporters on a call. “Opening up payments on these stores is essential to eliminating the ingrained advantage” that both Apple and Google app stores have on mobile devices.

Gatekeeper

Apple’s position as a gatekeeper for what apps can appear on iPhones or iPads has already attracted EU antitrust scrutiny. Regulators across the world are also increasingly concerned about the control some large internet platforms have over smaller firms that depend on them.

Epic is already suing Apple in the US and Australia and also filed complaints about Apple and Google app stores at the UK’s antitrust tribunal.

READ MORE: US judge: Apple could bar Epic Games' Fortnite from app store

Apple said in a statement that “Epic enabled a feature in its app which was not reviewed or approved by Apple, and they did so with the express intent of violating the App Store guidelines that apply equally to every developer and protect customers.” It said Epic’s “reckless behavior made pawns of customers, and we look forward to making this clear to the European Commission.”

The EU complaint could add to a commission investigation started last year into whether Apple violates competition law by forcing software makers to use its own in-app payment system. The EU’s antitrust arm is also probing a Spotify Technology SA complaint that Apple unfairly squeezes its music-streaming service and similar issues with e-books.

“Apple should not use its control of the hardware to force developers or consumers to use other Apple services by blocking all competitions,” Sweeney said. “There are large parts of the tech industry that cannot develop because of these monopolies.”