The ongoing battle between Apple and Fortnite gaming company Epic hit a milestone this week as Apple unveiled a proposed witness list for its upcoming trial. The tech giants are involved in a mobile app payment war that began last August when Apple kicked Fornite out of its App Store.

The move came after Epic Games added a crafty in-game payment system that bypassed Apple's payment mechanism for in-app purchases, cutting out Apple's commission of 30 percent of in-store payments. Apple argues that Epic broke its App Store agreement, while Epic has accused Apple of monopolist practices regarding mobile payments. Epic filed a lawsuit against Apple, internally codenamed "Project Liberty."

Witnesses on Apple's side include CEO Tim Cook, along with Craig Federighi, software engineering SVP, and Phil Schiller, an Apple Fellow. Witnesses for Epic will include CEO Tim Sweeney and Mark Rein, VP. Executives from Microsoft, Facebook and Nvidia will also testify at the upcoming trial, scheduled to begin May 3.

"We feel confident the case will prove that Epic purposefully breached its agreement solely to increase its revenues, which is what resulted in their removal from the App Store," wrote Apple in a statement. "By doing that, Epic circumvented the security features of the App Store in a way that would lead to reduced competition and put consumers’ privacy and data security at tremendous risk."

For its part, Epic spent months preparing the suit against Apple, which it announced publicly within hours of being removed from the App Store. Sweeney said the suit is meant to open up Apple's platforms to smaller developers, and that he believes open platforms are "the key to free markets and the future of computing."

Epic is one of the few companies with the financial independence to take on platforms like Apple and Google, and the company has spent considerable time and resources on the lawsuit. Sweeney said it has been worth it for Epic due to fears that the App Store will be dominated by platform owners like Apple in the future, financially closed off to smaller companies and developers.

"[The companies] will just do that industry by industry and app category by app category until they've gobbled up everything that matters. And who will be left?" asked Sweeney. "A million indie developers who collectively together make a small percentage of revenues on the app store because these businesses are too small to be attractive to steal."

Epic has also filed a complaint against Apple in the UK, claiming the removal of Fortnite from the App Store was unlawful. In both suits, the company is not asking for damages from Apple and states it is seeking "fair access and competition that will benefit all consumers."