The Government has been warned it risks a humiliating defeat on flagship Brexit Legislation if it does not accept the demands of up to 20 Conservative backbenchers.
The group are ready to revolt against ministers by backing an amendment to the EU Withdrawal Bill, which calls for a "meaningful" vote on any Brexit deal.
But, speaking hours before a possible vote, Theresa May rejected an offer to accept the amendment "in the spirit of unity".
Answering potential Tory rebel Anna Soubry at Prime Minister's Questions, Mrs May warned the amendment could put at risk an "orderly and smooth exit from the EU".
She suggested the planned change to the Brexit legislation would bar the Government from preparing to put in place a divorce deal and agreed transition phase until a "very late stage in the proceedings".
The Prime Minister also repeated her commitment to holding a meaningful vote, with Brexit Secretary David Davis having confirmed the Government's intention to do so in a written statement to Parliament earlier.
Mr Davis also penned a last-gasp letter to Tory MPs early on Wednesday morning as ministers battle to avoid a defeat.