Britain’s parliament is holding the first of what could be three days of votes Tuesday in order to decide how to proceed with its divorce from the European Union.

Members are voting Tuesday on Prime Minister Theresa May’s latest version of her plan, based on an agreement her government reached with the EU last year.

It initially got little support when first put to a vote, but May made a last-ditch trip to Strasbourg on Monday to secure altered terms in talks with EU Commission President Jean-Claude Juncker that she hopes will win over her opponents.

May said Juncker announced “legally binding changes” that in part address the longtime sticking point involving what to do with the border between Britain’s Northern Ireland and EU member Ireland.

The original deal calls for a so-called backstop agreement that keeps Britain and the EU in a customs union until they agree on a new trade agreement. Opponents in Britain’s parliament are concerned about being locked into EU rules instead of being able to gain full control of trade policies.

May said the new terms agreed to Monday would ensure the backstop deal is not a permanent part of Britain’s exit from the EU.

The opposition Labour Party rejected the plan, saying it still does not go far enough to allay their concerns.

Juncker warned that Britain is running out of options for Brexit, which is set to take place March 29.

“It is this deal or Brexit might not happen at all,” he said.

If the Brexit agreement fails the Tuesday vote, another would be held on Wednesday to see if lawmakers approve of exiting the EU at the end of the month with no terms in place. If that fails too, a third vote would come Thursday on whether to ask the EU for more time.