LONDON (Reuters) - British Prime Minister Theresa May’s attempts to get her Brexit deal approved by parliament must clear an early hurdle on Tuesday, when lawmakers try to force the government to hand over more power to parliament if the current deal is voted down.

May will later on Tuesday open a five-day debate on the terms of Britain’s withdrawal from the European Union which will culminate next Tuesday in several votes that, if lost, could cast her Brexit plans into disarray less than four months before ‘exit day’.

But, before May even stands up to speak, she could face a procedural challenge that would give parliament more power to dictate the government’s next steps if it loses the vote on whether to approve her deal.

A group of mainly pro-EU lawmakers from May’s Conservative Party, who want to prevent Britain leaving the EU without a deal, have proposed a procedural change that could avert such an outcome if May loses the vote.

Local media reported that the plan will be accepted for discussion. Advocates of the change want parliament to vote on it ahead of the main Brexit debate, as part of a procedural discussion.

The number of Conservative lawmakers already signaling their support for it, along with the expected support of the opposition Labour Party, means it has a strong chance of passing.

If successful, the challenge could potentially neutralize May’s threat to leave the EU without a deal if her deal is rejected - an important lever that she has been using to persuade some within her party to back her.

Currently, if the government loses the vote to approve the deal, its only obligation is to present a plan setting out its next steps to parliament within 21 days. Parliament would then be able to debate that plan, but could not propose alternatives or tie the government’s hands.

The rebel lawmakers, led by former attorney general Dominic Grieve, want to change that rule to say that parliament could propose and vote on alternative outcomes in the event the original deal is voted down.