The highest U.K. court ruled Prime Minister Theresa May must seek an act of Parliament to trigger the two-year countdown to Brexit, handing lawmakers a chance to soften the government’s plan.

The court ruled against the government by an 8-3 vote, Judge David Neuberger said Tuesday. The judges ruled unanimously, however, that legislatures in Scotland and Northern Ireland don’t get to vote on the Article 50 process that starts to wrest the U.K. from the European Union after 44 years.

The judges said leaving the EU will mark a fundamental change to British law by altering legal rights and cutting off EU laws. The U.K.’s constitutional arrangements require such changes to be clearly authorized by parliament, and lawmakers must be involved in triggering Article 50 of the Lisbon Treaty, they ruled.

“Only legislation which is embodied in a statute will do,” Neuberger said. “A resolution of the House of Commons is not legislation. What form such legislation should take is entirely a matter for Parliament.”

The decision is a defeat for May’s argument that she alone had the power to begin the country’s withdrawal from the EU. The need to now win the approval of lawmakers threatens her March 31 deadline for starting the divorce talks, although most legislators say they won’t try to stop the breakup given 52 percent of voters backed it in June’s referendum.

“Only Parliament can grant rights to the British people and only Parliament can take them away,” Gina Miller, who brought the case, said outside court. “No Prime Minister, no government can expect to be unanswerable and unchallenged.”

Five Stages

A bill to implement Article 50 will have to go through five stages in each of the two chambers of Parliament. Although it’s possible to pass emergency legislation in as little as one day, it is rare and the process can take months. There are votes at each stage, and lots of opportunities for dissenters to propose amendments. Both houses must agree on the wording of the final law.

The March 31 deadline “now seems in danger,” ex-U.K. Attorney General Peter Goldsmith said. “The ability of the government to put through an Act of Parliament without causing further delay in the timetable will surely be strongly tested in the coming weeks.”

Parliamentary critics of May, including some within her own Conservative Party, can seize the opportunity to shape her strategy amid concern she risks hurting the economy by jeopardizing trade to win control of immigration.

50 Amendments

May plans to rush through a short bill, designed to keep her timetable on track and give as little scope for amendments as possible.

The ruling that politicians in Scotland, Wales and Northern Ireland didn’t need to have a say before talks are triggered will be some comfort to May, as Scotland probably would have voted to block leaving the EU.

The Scottish National Party said it would make 50 amendments, including one which would require May to include the semi-autonomous governments in Scotland, Wales and Northern Ireland in its Article 50 decision.

The pound fell 0.4 percent to 1.2481 pounds after the ruling. Sterling had rallied last week when May said she would give Parliament a vote on the final deal she negotiates with the EU. But by the time they vote on the final settlement, with the two-year talks deadline approaching, the choice they will face will be between accepting the terms or allowing Britain to fallout of the bloc without a deal.

Softer Brexit?

Analysts said the ruling increases the chances of a so-called soft Brexit where the U.K. remains in the EU’s single trading market. The decision is “a positive for the long-term U.K. economic outlook,” according to Kallum Pickering, an economist at Berenberg Bank in London.

“MPs will likely nudge government toward a softer Brexit — one that prioritizes EU single market access over migration controls — to get the bill over the line,” Pickering said.

The three dissenting judges argued that although parliament needed to be involved in the process, that didn’t require legislation.

One of the judges, Robert Carnwath, said that European treaties and laws would now need to be reversed.

“On any view, the legal and practical challenges will be enormous,” he wrote.

The government had hoped to avoid a vote for fear lawmakers would bog down her plans. A majority in the lower chamber, the House of Commons, supported remaining in the EU and many members of the unelected upper chamber, the Lords, have also expressed concerns.

The chance of amendments rose last week after May pledged to leave the EU’s single market to win control of immigration and lawmaking — essentially a so-called hard Brexit.

Labour Party leader Jeremy Corbyn said that while the opposition won’t frustrate Article 50, it will try to amend the bill. He aims to “build in the principles of full, tariff-free access to the single market,” to ensure the government is accountable to Parliament through the negotiations and to put the final deal to a “meaningful” vote.

Tim Farron, the leader of the Liberal Democrats, former coalition partners of May’s Conservatives when her predecessor David Cameron was premier, said his party will vote against Article 50 unless the government agrees to subject the ultimate Brexit pact to a referendum.

More Cases

Any hope the Supreme Court’s ruling might herald an end to May’s legal headaches are likely to be disappointed, as at least two new challenges gather pace.

A Dublin court is being asked if the two-year exit process can be terminated at a later date, while two campaigners filed a lawsuit claiming the referendum didn’t grant May the authority to pull Britain from the European single market.

The politically charged lawsuit has placed the most senior judges in the British judiciary, a group traditionally reluctant to stray into politics, in uncharted territory.

The Supreme Court heard testimony at the start of December after the government appealed a November ruling by the High Court.

The case was initiated Miller, who runs an investment start-up, and Deir Dos Santos, a hairdresser. Separate claims brought by others were consolidated behind Miller’s, who became the public face of the lawsuit and has endured death threats.

“I sincerely hope that going forward, people who stand in positions of power and profile are much quicker in condemning those who cross the lines of common decency,” Miller said.

Some U.K. newspapers cried foul over the High Court’s decision, saying that judges had no place meddling in a democratic process.

The Daily Mail featured pictures of the three judges on its front page and the headline, “ENEMIES OF THE PEOPLE.” The Daily Telegraph billed the ruling as the “Judges Versus the People.”

The British public voted to leave the EU in a June 23 referendum, causing David Cameron to quit as prime minister and May move in as his successor.