(Pocket-lint) - Weeks after Epic Games sued Apple for removing Fortnite from the iOS App Store over an update that added an unauthorized payment system, Apple has officially filed to countersue. The complaint seeks damages against Epic Games for allegedly breaching its contract with the iOS App Store.

“Epic’s flagrant disregard for its contractual commitments and other misconduct has caused significant harm to Apple,” Apple's filing reads. “Left unchecked, Epic’s conduct threatens the very existence of the iOS ecosystem and its tremendous value to consumers.” Keep in mind Epic's complaint, filed 13 August, asserts that Apple is violating antitrust law, by abusing its dominance and complete control of iOS to charge high commissions.

Apple's 8 September filing details various defenses against Epic Game's latest motion for a preliminary injunction, which was filed over the weekend. Apple even alleges its response to Epic Games can be justified. “At all times, [Apple’s] conduct was reasonable and . . . its actions were undertaken in good faith to advance legitimate business interests and had the effect of promoting, encouraging, and increasing competition,” the complaint reads.

Meanwhile, Epic Games has announced that Apple’s “Sign In with Apple” login system will no longer work with Epic Games accounts as soon as 11 September. That means you’ll need to update your account with new login credentials before then to maintain access. Epic has a guide on how here. Epic said it might be able to help recover accounts after the “Sign in with Apple” option expires, but you’ll have to contact the studio first.

Apple booted hit game Fortnite from the iOS App Store on 13 August, when Epic introduced an in-app payment system that violated Apple’s rules. Epic Games' reply to Apple’s latest filing is due by 18 September. A full hearing for the two companies is set for 28 September.

Writing by Maggie Tillman.