Frontier Developments is currently suing Atari for royalties owed from a 2004 collaboration.
As part of the deal, Frontier was entitled to a share of the royalties, and when Atari went bankrupt in 2013 the studio amended its contract and "stuck it out". The studio has since discovered through "another website" that sales for the game were higher than they had previously thought. So while it had already received $1.17m, it allegedly should have been paid $3.37m - a difference of $2.2m.
The studio also claims Atari delayed when Frontier requested an audit of its sales reports. The firm is now suing for the royalties owed.
"We have attempted to resolve this issue without legal action since April 2016," COO David Walsh told Eurogamer. "We have so far been denied our contractual right to audit by Atari, and we are unfortunately left with no other way to resolve our concerns."
Frontier has recently competed directly with Atari's latest theme park title RollerCoaster Tycoon World with the release of its own Planet Coaster in late 2016.
Atari has previously sued series creator Chris Sawyer back in 2007, claiming he had worked with Frontier to develop an enhanced version of RollerCoaster Tycoon 3 - despite Atari still owning the rights to create and market new titles in the franchise. That particular dispute ended with an out of court settlement.