LONDON (AP) — British Prime Minister Theresa May said Thursday she may let Parliament decide whether to trigger the controversial Northern Ireland "backstop" as she shrugged off suggestions that the government may delay a vote on her Brexit deal to avoid a stinging defeat.

The proposal, designed to ensure there is no hard border on the island of Ireland, has sparked opposition from all sides because of concerns it would drive a wedge between Northern Ireland and the rest of the U.K. while leaving the country tied to the European Union indefinitely. A vote on the deal is scheduled for Tuesday.

May stressed in an interview with the BBC that the backstop is an insurance policy that would only be used if the two sides can't hammer out an agreement on future relations by the end of 2020, and that it would be up to the U.K. to decide whether to invoke the provision.

"There would be arguments on different sides at that point in time," she said. "I think people are concerned about the role of the U.K. in making these decisions, and the obvious (thing to do) in terms of the role of the U.K. is for it to be Parliament that make these decisions."

May's effort to win support for her Brexit agreement comes amid reports in British newspapers that Parliament could reject the deal by more than 100 votes. Lawmakers are opening a third day of debate on the measure Thursday, focusing on economic issues.

As she doggedly presses on, May is sticking to her mantra that the deal she negotiated over the past 2½ years will allow the U.K. to take back control of its money, laws and borders. The agreement is the only way to avoid a no-deal Brexit that would have dire consequences for the economy and head off those who are trying to use the debate to prevent the country from leaving the EU, she said.

"There are those who want to frustrate Brexit and overturn the vote of the British people," May told the BBC. "That's not right."

But May is facing opposition from both sides of the Brexit debate.

Lawmakers who favor leaving the EU say the prime minister's deal keeps Britain bound too closely to the bloc while those who want to maintain close ties argue that it creates barriers between the U.K. and its biggest trading partner.

Both sides also worry the deal leaves many of the details of the future relationship to further negotiations that will take place after Britain leaves on March 29.

Looming over those talks would be the backstop, which could leave the U.K. in a customs union with the EU indefinitely if negotiators fail to agree on another way to prevent border checks on goods and people passing between Northern Ireland and the Republic of Ireland. Legal advice released Wednesday underscored the fact that the U.K. wouldn't be able to leave the backstop without approval from the EU, hardening opposition to the deal.

Amid fears that time is running out, some lawmakers are looking to the European Court of Justice for help.

The court is scheduled to rule Monday on whether Britain can change its mind about leaving the EU. A top adviser to the court earlier this week issued a non-binding opinion that the U.K. can unilaterally revoke its decision to leave.

Campaigners say unilaterally revoking Brexit could give Britain the option to "stop the clock," giving the country an alternative to the options of May's deal or no-deal. The case comes as pressure builds for a second referendum, something May has ruled out citing the 52 percent of population that voted for Brexit in 2016.

"A lot of the people who are calling for a referendum want that because they hope that there's going to be a different answer," May said. "I don't think that's right. We asked people the question; they gave us the answer. Let's deliver on that first vote."