Frontier Developments, developer of Planet Coaster, Elite Dangerous and Screamride, are suing Atari over unpaid royalties, TMZ reports.

Frontier is reportedly owed $2.2m in royalties over Atari’s 2004 RollerCoaster Tycoon 3 title. The company had already received $1.17m in royalties based on RollerCoaster Tycoon 3’s sales figures, but in April 2016 “another website” reported the game had sold more units than they were led to believe. Frontier claims they should have received $3.37m in total.

Speaking to Eurogamer, Chief Operating Officer David Walsh revealed Frontier had attempted to resolve the issue with Atari privately since April 2016. Walsh claims that Frontier have been denied their right to audit Atari’s sales data and have been left with no choice but to pursue the matter via the courts.

Interestingly, the two companies went head-to-head last year on the sales charts with Frontier releasing Planet Coaster and Atari releasing RollerCoaster Tycoon World. The former has received critical acclaim while the latter has received a mostly negative reception.