The U.K. Supreme Court has dismissed Mastercard’s appeal in a long-running case that could result in it having to pay £14 billion in compensation to millions of consumers, and one that could pave the way for future class actions.

On Friday, the Supreme Court said it “agrees with the Court of Appeal” decision that the Competition Appeal Tribunal’s (CAT) decision was “undermined by error of law”. The matter will now be sent back to to the CAT.