The makers of PlayerUnknown’s Battlegrounds have accused the makers of Fortnite of copyright infringement. They’ve filed a legal complaint specifically over the Battle Royale mode.

The legal action comes from the developer, the South Korean company PUGB, against Epic Games of the US, though the case has been filed in Korea against the local Epic Games subsidiary.

Exactly what the legal action involves and the resulting process isn’t entirely clear, but reports from The Korea Times suggest PUGB originally filed a copyright complaint in January and then followed it up with a request for an injunction last week.

It’s not a major surprise as the makers of PUGB complained publicly as soon as Fortnite’s Battle Royale mode launched last September. They said the mode unfairly copied “items”, “core elements” and the “user interface.”

It’s a particularly awkward situation as PUBG is based on a game engine licensed from Epic Games.

Epic Games has yet to publicly comment on the claims or the legal action.