LONDON (AP) — Mastercard could have to pay U.K. consumers as much as 14 billion pounds ($18.5 billion) after the country’s Supreme Court allowed a class-action lawsuit against the credit-card company to move forward.

The Supreme Court on Friday ordered a competition tribunal to reconsider its decision to block a lawsuit alleging that Mastercard overcharged businesses that accepted the company’s credit and debit cards.

These fees were then passed on to consumers in the form of higher prices, the suit claims. Mastercard does not accept that merchants passed on all or any part of any overcharge to their customers.

The Competition Appeal Tribunal must now reconsider its refusal to certify the lawsuit as a “collective proceeding.” Certification is required before mass litigation can proceed in Britain.

The tribunal initially accepted Mastercard’s position that the claims weren’t eligible for collective proceedings. But the Court of Appeal found that the tribunal had misinterpreted the law and ordered it to reconsider the case. Mastercard appealed to the Supreme Court, which upheld the appellate court ruling.

In his decision, Justice Michael Briggs said the panel shouldn’t have blocked a trial just because it would be “burdensome and expensive” to compile data on the alleged overcharges.

Walter Hugh Merricks, the former head of the U.K.’s Financial Ombudsman Service, filed the lawsuit after the European Commission ruled that some fees charged by Mastercard between 1992 and the end of 2007 were too high and restricted competition.

The suit claims that consumers were overcharged by 14 billion pounds during this period and seeks a payment of about 300 pounds for everyone who was over 16 and lived in the U.K. at the time.

The Supreme Court said the damage figure was likely to be a “considerable over-estimate.” Even so, the disparity between the relatively small size of individual damages, compared with a potentially large collective recovery, make this case “completely unique” in the U.K. courts, Briggs wrote.

“Collective proceedings are a special form of civil procedure for the vindication of private rights, designed to provide access to justice for that purpose where the ordinary forms of individual civil claim have proved inadequate for the purpose,” he said.