Apple has abused its dominant position by charging app developers an unfair 30% commission through its App Store, costing British consumers up to 1.5 billion pounds ($1.8 billion), a London tribunal heard on Monday.

Apple is under trial at London’s Competition Appeal Tribunal, accused of exploiting its dominance by overcharging app developers a 30% commission through its App Store. The lawsuit, representing 20 million UK iPhone and iPad users,

Lawyers representing the class action said that Apple excluded potential rivals from competing for customers on devices running its iOS operating system by forcing developers to sell their apps exclusively through its own App Store and charging commissions of 30% for purchases.