British prime minister Theresa May will make the case for her new Brexit plan in Parliament later, amid signs that Conservative opposition to her leadership is hardening.
The premier will give a statement to MPs on her changes to the Withdrawal Agreement Bill - including her promise to give MPs a vote on holding another referendum.
But Labour MPs said too little had changed for them to come on board.
And one ex-Tory minister questioned whether June's vote would even happen, according to a BBC report Wednesday.
MPs have rejected the withdrawal agreement negotiated with the EU three times, and attempts to find a formal compromise with Labour have failed.
On Tuesday, the prime minister asked MPs to take "one last chance" to deliver a negotiated exit - or risk Brexit not happening at all.
But Mrs May's new plan had "failed to turn sceptics into endorsers", said BBC political correspondent Chris Mason.
Conservative MP Boris Johnson - who wants to succeed Mrs May as prime minister - said on Twitter: "We are being asked to vote for a customs union and a second referendum. The Bill is directly against our manifesto - and I will not vote for it.
"We can and must do better - and deliver what the people voted for."
Meanwhile Dominic Raab, another leadership hopeful, said Mrs May's deal would "break our clear manifesto promises".