A case has been filed against Apple in the UK Competition Appeal Tribunal (CAT) citing the 30 per cent margin charged on App Store payments.
The organizers have estimated 20 users are affected in the UK, and are aiming for $2.1 billion compensation from Apple if the case is approved.
Anyone who has made a purchase on the iOS since October 2015 can be included in this claim.
The move comes at a difficult time for Apple; notably its increasingly high profile case against Epic Games in the US.
Dr Rachael Kent, a digital-economy lecturer at King's College London, is leading the case supported by law firm Hausfeld and Co and Vannin Capital.
"This is the behaviour of a monopolist and is unacceptable. It would not be able to impose these exorbitant charges if competitor platforms and payment systems were allowed to compete," Dr Kent argued.
In defence, Apple has commented the legal action is meritless.
"We believe this lawsuit is meritless and welcome the opportunity to discuss with the court our unwavering commitment to consumers and the many benefits the App Store has delivered to the UK's innovation economy."