Mastercard may be required to pay up to 14 billion pounds ($18.5 billion) after the UK Supreme Court allowed a class action lawsuit to go forward Friday. The lawsuit, which covers 46 million UK adults, was initially blocked by the Competition Appeal Tribunal (CAT) on grounds that the class action case would be too complex or expensive to try. Based on the Supreme Court’s instructions, the CAT will now reconsider its decision to grant certification to the class action lawsuit, potentially allowing the suit against Mastercard to move forward.

Mastercard allegedly overcharged merchants for use of Mastercard’s debit and credit cards between 1992 and 2008, and plaintiffs argue that the additional costs were passed on to consumers. While the Supreme Court stated that 14 billion pounds in damages is likely an over-estimate, this landmark decision could be followed by an increase in class action lawsuits in the UK, a country that has so far shown hesitancy in allowing collective actions.

The CAT was nominated to handle “opt-out” class action suits in 2015 after the Consumer Rights Act was passed. The opt-out system, widely implemented in the US, is a new approach to legal action in the UK, where plaintiffs in a certain group will be automatically included in a class-action suit unless they specifically opt out.

Critics of the opt-out system point to the litigation-heavy culture in the US as a potential downfall of allowing such class action lawsuits. But proponents believe that such collective lawsuits can hold large companies accountable in a way that that would not be ordinarily possible if only individuals were suing the company. Certainly, this suit against Mastercard will be the first to test a new consumer-focused legal approach in the UK.