Labour peers could hold a vote of no confidence in Jeremy Corbyn’s leadership over his response to claims of anti-Semitism in the party.
This follows the sacking of Baroness Hayter – a critic of Mr Corbyn over the issue – as Brexit minister.
The BBC understands Labour peers will hold an emergency meeting on Monday to consider a motion calling for a no-confidence vote.
If passed, a ballot of all Labour peers will follow.
The result would not affect Mr Corbyn’s position, however, as it is an expression of opinion rather than in any way binding.
But BBC assistant political editor Norman Smith said such a vote would be “extraordinary and unprecedented”.
It is understood there is widespread anger among Labour peers at the sacking of Baroness Hayter after she reportedly compared the approach of Mr Corbyn’s staff to that of “the bunker” in Downfall, a 2004 film depicting Adolf Hitler’s final days.
The peer was critical of Mr Corbyn’s inner circle, who she claimed had refused to give the party’s ruling National Executive Committee key information on party finances, membership figures and anti-Semitism data.
Baroness Hayter was also was one of four peers who wrote to Mr Corbyn earlier this week calling for an inquiry into allegations in the BBC’s Panorama that senior figures in the party had interfered in the disciplinary process of dealing with accusations of anti-Semitism.
She was cheered by both sides of the House of Lords on Thursday when she entered the chamber and took her place on the Labour back benches.
Speaking to Radio 4’s World at One, Baroness Hayter said she had not “heard from” Labour’s leadership to tell her she had been sacked, but the news had been released to the Corbyn-supporting news blog Skwawkbox.
She added: “I haven’t been asked to apologise.”
Baroness Hayter also said: “I’ve always supported Jeremy Corbyn since he was elected.”
A Labour Party spokesman said that Baroness Hayter had been sacked “for her deeply offensive remarks about Jeremy Corbyn and his office”.
He added: “To compare the Labour leader and Labour Party staff working to elect a Labour government to the Nazi regime is truly contemptible, and grossly insensitive to Jewish staff in particular.”
Baroness Hayter remains Labour’s elected deputy leader in the House of Lords, as this – unlike the role of shadow Brexit minister – is an elected, rather than appointed, position.