Sony PlayStation is being sued for £5bn in the UK over allegations it "ripped off its customers" with overpriced games and in-game purchases.
The group legal action, led by consumer rights champion Alex Neill, could see almost nine million gamers compensated.
It claims Sony PlayStation breached competition law, imposing unfair terms and conditions on games' developers and publishers, and driving up prices.
"The game is up," said Ms Neill. Sony PlayStation has yet to comment.
The claim, filed at the Competition Appeal Tribunal, alleges the gaming company abused its position as the market leader to impose terms and conditions on games' developers and publishers, including a 30% commission on every digital game or in-game purchase made through the online PlayStation Store.
The legal case claims Sony PlayStation's actions have driven up prices for consumers, resulting in customers being "unwittingly overcharged" for digital gaming purchases by up to a total of £5bn over the past six years.