The escalating battle between Apple and Epic Games has already resulted in Fortnite being unavailable to download on phones around the world. 

But if Apple disables Epic’s developer account, then the company won’t be able to maintain the Unreal Engine for iPhones and other Apple computers, which Epic sees as an “existential threat.”

Investors believe that the potential of the Unreal Engine and its ubiquity is a large part of Epic Games’ $17.3 billion valuation.