Amazon.com Inc is facing a lawsuit in Britain for damages of up to £900 million ($1 billion) over allegations the online marketplace abused its dominant position by favouring its own products, lawyers said.

Consumer rights advocate Julie Hunter plans to bring a collective action on behalf of British consumers who have made purchases on Amazon since October 2016, lawyers representing her said.

The proposed case — which Amazon said was “without merit” — would be the latest mass action against a tech giant to be filed at London’s Competition Appeal Tribunal (CAT).

Law firm Hausfeld, which represents Hunter, said on Thursday that Amazon had breached competition law by using “a secretive and self-favouring algorithm” to promote its own products through the “Buy Box” feature on its website.

Hunter said in a statement: “Far from being a recommendation based on price or quality, the Buy Box favours products sold by Amazon itself, or by retailers who pay Amazon for handling their logistics.

Other sellers, however good their offers might be, are effectively shut out.”

An Amazon spokesperson said: “This claim is without merit and we’re confident that will become clear through the legal process.”