The US justice department wants to have its say on Apple's antitrust tussle with Epic Games, which is due to be heard on appeal next month -- a year after a Californian court ruled largely in favor of the iPhone maker.

On Friday, the appeals court granted the department the right to send a representative to the hearing scheduled for October 21, where both sides are expected to make their case again.

In 2021 a California judge ruled against Fortnite-maker Epic, which had accused Apple of acting like a monopoly in its shop for digital goods or services.

But the judge also barred Apple from prohibiting developers from including in their apps "external links or other calls to action that direct customers to purchasing mechanisms."

Apple can still mandate that its payment systems is used for in-app transactions.

Both sides are appealing.

Earlier this year the justice department asked for time at the appeal hearing to air concerns about the trial judge's interpretation of antitrust law at issue in the case.

"The district court committed several legal errors that could imperil effective antitrust enforcement, especially in the digital economy," justice department lawyers argued in their brief.

Justice officials have been investigating whether Apple and other tech giants are abusing their market clout with anti-competitive practices.

Attorneys for Apple, Epic and the justice department will all speak to the appeals court, which will also consider their written arguments.