×

Britain’s Supreme Court ruled Tuesday that only Parliament has the power to trigger the country’s exit from the European Union, not the government, dealing a blow to Prime Minister Theresa May but probably not impeding the withdrawal process.

To leave the E.U., Parliament has to invoke Article 50, the E.U. treaty provision that initiates a country’s exit. There will then be a two-year period of negotiation between Britain and the E.U. to determine the terms of the divorce.

May had argued that her administration could trigger the departure process, without having to seek approval from lawmakers. But the Supreme Court disagreed in an 8-3 ruling.

The court decision is unlikely to halt or significantly delay Brexit, because lawmakers in Parliament are expected to approve Article 50, which May wants to invoke by the end of March. But it does open the door for lawmakers to influence the terms under which the country leaves, such as whether the U.K. remains part of the E.U. single market.

May appears to favor a so-called “hard Brexit,” with Britain cutting virtually all ties with the E.U. But many members of Parliament favor a more moderate approach under which the country would maintain many economic ties, in order to have free access to the E.U. market.