Microsoft has submitted a declaration in Epic's court case, expressing support for the company's action against Apple.

Microsoft is supporting Epic Games, the company behind Fortnite, in its battle against Apple, according to a new legal declaration.

Epic is engaged in a serious corporate dispute with Apple after the iPhone maker took action against it for slipping a new payment system into the iOS version of the hit online shooter.

It is suing Apple to prevent it from revoking its access to iOS and MacOS development tools, which both Fortnite and even more crucially its Unreal Engine game engine depend on.

In a new court filing, Epic states that many of the thousands of other game developers who use the Unreal Engine had been in touch to express their concerns about the impact Apple's actions would have on their games.

Microsoft has now also filed a declaration in support of Epic, describing Unreal as "one of the most popular third-party game engines available to game creators".

"In Microsoft's view there are very few other options available for creators to license with as many features and as much functionality as Unreal Engine across multiple platforms, including iOS," the statement added.

The company also added a specific warning that its racing game Forza Street would be affected if developers were unable to maintain the Unreal code.

Microsoft is a powerful potential ally for Epic in its growing dispute about Apple's control over the App Store, and the company has previously criticised Apple for prohibiting its games-streaming service from the app store.

The company said Apple "stands alone as the only general purpose platform to deny consumers from cloud gaming and game subscription services like Xbox Game Pass".

"[Apple] consistently treats gaming apps differently, applying more lenient rules to non-gaming apps even when they include interactive content," Microsoft added.

Epic is currently bringing an anti-trust lawsuit against Apple in California, alleging that the tech giant exploits its monopoly over the App Store.

Epic is requesting a temporary restraining order against Apple to prevent it from revoking Epic's developer accounts, as Apple has pledged to do by 28 August, which Epic warned would cause the company "irreparable harm".

Apple described Epic's complaints as being about "self-inflicted wounds", stating that it would not take any action against Fortnite if the company removed the direct payment functionality it inserted into the Fortnite app.

The direct payment functionality was designed so that Epic could bypass the App Store's own payment system, which sees Apple take a cut of up to 30% from in-app purchases.

Purchases made via Epic's system were cheaper, which Epic claimed was a way of passing savings on to its players.

On Monday, the court will hold a hearing for a preliminary injunction Epic is requesting, which would require Apple to keep Fortnite available on the App Store until the lawsuit has concluded.