Jeremy Corbyn is struggling to contain a shadow cabinet revolt after the Labour leader said he could not support RAF air strikes against Islamic State in Syria.
As divisions among Labour's top team spilled out into the open, shadow ministers were warned they faced the wrath of grass roots activists unless they fell into line and back the leader.
The shadow cabinet will gather again on Monday to try to come to a common position after a stormy meeting failed to reach agreement on how they should respond to David Cameron's Commons statement setting out the case for attacking IS in its Syrian heartland.
Amid the growing crisis, Mr Corbyn has pulled out of a planned visit to campaign in the Oldham West by-election in order to deal with the situation.
With a majority of members now firmly in favour of air strikes, one of Mr Corbyn's few allies in the shadow cabinet warned they could expect to come under intense pressure when they return to their constituencies at the weekend.
Shadow international development secretary Diane Abbott insisted the shadow cabinet was not entitled to vote down the leader and said she was confident they would come to the "right decision".
"I know what views party members will take if MPs ignore the views of the people at the grass roots and try and take this issue to the brink," she said during a round of broadcast interviews.
"Jeremy appoints the shadow cabinet - not the other way round. You cannot have a shadow cabinet voting down the leader of the Labour Party who has just been elected with the biggest mandate in history."
There was anger among some Labour MPs after Mr Corbyn issued a letter following Thursday's meeting saying the Prime Minister had failed to make a "convincing case" and that he could not support further military intervention.
The move was seen by some as an attempt to pre-empt next week's shadow cabinet meeting while appealing over the head of MPs to the grass roots members who swept Mr Corbyn to the leadership.
His comments were in stark contrast to the shadow foreign secretary Hilary Benn who said Mr Cameron had set out "compelling arguments" for Britain to join other members of the US-led coalition in extending air strikes against IS into Syria.
The turmoil in Labour ranks complicate Mr Cameron's calculations as to whether he has got the numbers to win a Commons vote on extending air strikes against IS - currently restricted to Iraq - into Syria.
The Prime Minister has repeatedly said he will not seek the support of the House unless he is certain of winning as defeat would hand a propaganda victory to the extremists.
But with some Conservative MPs still opposed to further military intervention, he is likely to need the support of a significant number of Labour MPs to ensure he gets the outcome he wants.
For Mr Corbyn, the issue is whether he is prepared to risk a damaging revolt - and possible resignations - by trying to enforce his view or will agree to give Labour MPs a free vote in any Commons division.