Crytek, maker of the CryEngine game engine, is suing the team behind Star Citizen for breach of contract. This lawsuit, filed in U.S. district court in California, has the potential to disrupt development of a game that is already more than five years in development and has yet to deliver on many promises to its backers.

The complaint names Cloud Imperium Games (CIG) and Roberts Space Industries (RSI) as the defendants. Both companies were co-founded by Chris Roberts, the creator of the Wing Commander franchise.

As we explained in October, the Star Citizen project is actually an effort to create two unique AAA-quality games: an online multiplayer game referred to as the Persistent Universe and a single-player game called Squadron 42. Crytek said in its lawsuit that in continuing to use the CryEngine 3 for both products, CIG and RSI are in breach of contract.

In December 2016, CIG and RSI said they were moving off of CryEngine 3 in favor of Amazon’s Lumberyard product. But the complaint filed by Crytek says that’s not the case. Looking carefully at CIG and RSI’s own marketing materials, show lines of code on the screen that seem to indicate the games are running, at least partially, on CryEngine 3.

Making matters even more complicated is the fact that Amazon’s Lumberyard is, in fact, a fork of the CryEngine itself purchased by Amazon.

The lawsuit goes on to say that CIG and RSI improperly removed the CryEngine logo when the game boots up, and that the teams failed to properly disclose modifications to CryEngine 3 as part of their licensing agreement.

But the lawsuit doesn’t stop there. As we reported in 2016, CIG and RSI began selling two distinct games — Squadron 42 and the Star Citizen Persistent Universe. Crytek says that since both use the same code, that constitutes using the engine twice and represents a further breach of contract.

Crytek is asking for direct damages, indirect damages and a permanent injunction to prevent CIG and RSI “from continuing to possess or use the Copyrighted Work.” That could mean poring over the code of an incredibly complex game

Polygon has reached out to the Star Citizen team, Crytek and Amazon for comment.

Update (Dec. 13): As this story was published, a representative of CIG and RSI responded with the following comment:

“We are aware of the Crytek complaint having been filed in the US District Court,” the spokesperson said. “CIG hasn’t used the CryEngine for quite some time since we switched to Amazon’s Lumberyard. This is a meritless lawsuit that we will defend vigorously against, including recovering from Crytek any costs incurred in this matter.”

Update (Dec. 15): Overnight, Crytek responded to Polygon with the following statement:

“Crytek is a technology company and intellectual property is its greatest asset,” they said. “It is unfortunate that this lawsuit had to be brought, but Crytek has been left with no option but to protect its intellectual property in court.”

It seems that both side of the lawsuit are digging in.