Story broke by TMZ: http://www.tmz.com/2017/01/03/atari-video-game-royalties-lawsuit/
The suit is related to the development of RollerCoaster Tycoon 3 which Frontier developed for Atari back when Frontier was not self-publishing.
Apperantly the dispute is around how much RCT3 has actually sold. The article is refering to "a website" showing higher salesfigures than Atari was showing Frontier. Might this website be SteamSpy?