More than a year and a half ago, British Prime Minister Theresa May invoked Article 50 of the treaty that established the European Union, declaring the U.K.'s intention to become the first member to leave the international bloc. At the time, the move seemed to be a crossing of the Rubicon, an indelible step toward departure.

Now, the EU's highest court says the U.K. can cross back if it wants.

The Court of Justice of the European Union ruled Monday that the U.K. is allowed to reverse its decision to notify the EU of its intent to leave — and to do so entirely on its own, without the consent of the bloc's other member states.

That window for the U.K. is open so long as it hasn't implemented a final Brexit agreement with the EU — and would remain open until Article 50 was due to take effect on March 29, 2019.

The court's ruling comes at a precarious time for May, who had scheduled a vote Tuesday in the U.K. Parliament on the draft Brexit deal she negotiated with the EU. The prime minister announced Monday that she would be postponing that vote, acknowledging that the deal currently does not have the support necessary for the deal's approval.

May's draft deal has taken flak from nearly all sides of the U.K. political spectrum, including from within her own Conservative Party.

The crux of the Conservative frustration rests with the status of Northern Ireland, which is part of the U.K. but also shares an open land border with the Republic of Ireland, an EU member. Northern Ireland would be placed under different customs regulations than the rest of the U.K. if London and Brussels cannot agree on a future trade relationship. Conservatives have dismissed the that as subjecting the region to unwelcome EU oversight.

Some members of Parliament who campaigned against Brexit have called for a second referendum on Brexit.

Meanwhile, Nicola Sturgeon, Scottish National Party leader and first minister of Scotland, said Monday that if Labour Party leader Jeremy Corbyn introduces a motion of no-confidence in May's government, Sturgeon's party would support the measure.

"We can then work together to give people the chance to stop Brexit in another vote," she tweeted, tagging Corbyn. "This shambles can't go on — so how about it?"

It is not the first time lawmakers have suggested introducing a vote of no-confidence in May. Members of May's own party floated the idea of a no-confidence vote on her leadership of the Conservative Party last month, but it died from a lack of support.

The tumult has placed May's government between a rock and a hard place, between those who want to renegotiate the departure deal and others who demand the right to reverse the departure entirely.

Meanwhile, representatives of the European Union have remained steadfast that the draft deal — which European leaders have already approved — is the only one on the table.

"As [European Commission President Jean-Claude] Juncker said, this deal is the best and only deal possible," a commission spokesperson said, according to the BBC. "We will not renegotiate — our position has therefore not changed and as far as we are concerned the United Kingdom is leaving the European Union on 29 March, 2019."

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