Britain's Prime Minister Theresa May leaves 10 Downing Street in London, June 6, 2018. REUTERS/Toby Melville

QUEBEC CITY (Reuters) - British Prime Minister Theresa May urged lawmakers to back the legislation that will end Britain’s membership in the European Union, ahead of a series of crunch parliamentary votes that could see a rebellion by those who want closer EU ties.

May’s Brexit plan will begin its most severe test to date on June 12 when she asks her divided Conservative Party to overturn changes made to the European Union (Withdrawal) Bill by parliament’s upper chamber.

“I hope what everybody will see when they come to vote next week is the importance of ensuring that we get the EU withdrawal bill onto the statute book, because it’s that EU withdrawal bill that ensures that we’re able to have that smooth transition when we leave the European Union,” May said, speaking to reporters on Thursday during a flight to Canada, where she will attend the G7 summit.

The most contentious changes centre on Britain’s future economic relationship with the EU. Namely whether Britain should leave the EU’s customs union, as May wants, or stay closely aligned with the bloc’s border regime, as some members of her party want.