Parliament must approve the government’s plan to start the Brexit process, the United Kingdom’s Supreme Court ruled.

That means Prime Minister Theresa May can’t give notice to the European Union of the UK’s intent to withdraw nor begin negotiations to that effect until lawmakers back the move.

The conventional wisdom has it that Parliament will do just that—and before the government’s schedule to formally notify the EU by the end of March.

The basis of the court’s ruling—which backed an earlier decision by a lower court—was that invoking Article 50 of the Lisbon Treaty and triggering exit negotiations with the EU involves overturning UK law that Parliament approved in 1972, so it takes an act of Parliament to undo Britain’s ties to the continent.

The government argued that Parliament put the questions in the hands of the people, who voted last June in favor of Brexit by a margin of 51.9 percent to 48.1 percent. But it was always understood that the Brexit referendum was not legally binding. The Supreme Court’s decision was not unexpected.

Observers expect that the Conservative government will soon introduce some very pithy legislation to actualize the result of the Brexit referendum, hoping it will be approved within two weeks. But opposition leaders say they will introduce amendments that could delay or even hamstring the passage of the measure. Labour leader Jeremy Corbyn, while denying any desire to frustrate the process said his his party would “seek to…prevent the Conservatives using Brexit to turn Britain into a bargain basement tax haven off the coast of Europe.”

The Scottish National Party said it would put forward amendments requiring the government to release a white paper detailing its negotiating aims and to consult with the Scottish, Welsh, and Northern Irish governments. In its decision, the Supreme Court ruled that these “devolved administrations” need not approve of the Article 50 legislation.

Other opposition parties said their may oppose the Article 50 measure.

The Brexit process has had its twists and turns over the last few months. Prime Minister Theresa May, originally a Brexit opponent, is now all-in with Article 50.

No one expects Parliament not to approve the government’s legislation. But then again no one expected British voters to approve Brexit.