Willkie Farr & Gallagher is acting on a £1 billion collective action against Amazon at the Competition Appeal Tribunal (CAT) in London, the biggest suit to have ever been launched by U.K. retailers.

The damages claim is being brought by the British Independent Retailers Association (BIRA) on behalf of retailers on Amazon’s U.K. marketplace, according to a statement by the firm. It accuses the American multinational of ”illegally misusing their data and manipulating the Amazon Buy Box” for the company’s own commercial benefit, between October 2015 and now.