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 was accused Monday of abusing the dominant position of its app store at the start of a court trial in the UK, with plaintiffs seeking £1.5 billion ($1.8 billion)

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.

Apple is facing a massive legal battle in the UK over its App Store fees. Here's everything you need to know about the lawsuit.