Theresa May is launching a fresh push to convince MPs to back her Brexit deal as they begin five days of debate.
The prime minister cancelled a vote on her deal last month at the last minute to avoid a humiliating defeat.
She is hoping new proposals on Northern Ireland will change enough MPs’ minds to save the deal.
But the DUP have already rejected the plans – and rebel Tories are planning a move that could give MPs more say over what happens if her deal is rejected.
The MPs, headed by former Tory ministers Oliver Letwin and Dominic Grieve, helped inflict a defeat on the government on Tuesday on an amendment aimed at making it more difficult to leave the EU without a deal.
Now they are planning to table another amendment that could open up alternatives to Mrs May’s deal if she loses next week’s vote.
The amendment, to a procedural motion, has been selected for debate by Speaker John Bercow, at about 1300 GMT, after Mrs May faces Jeremy Corbyn at Prime Minister’s Questions.
The government is understood to be examining ways of challenging Mr Bercow’s decision.
Labour has, meanwhile, said it will table a motion of no confidence in the government if Mrs May’s deal is voted down next week.