Labour is on the brink of a split, with a group of MPs expected to resign from the party in protest at Jeremy Corbyn's leadership over Brexit.
Simmering tensions within Labour ranks over Mr Corbyn's approach to leaving the European Union and the party leadership's handling of anti-Semitism allegations are expected to result in a schism.
A group of the party's MPs will make a statement "relating to the future of British politics" on Monday morning.
Key figures believed to be on the verge of leaving did not respond to requests for comment.
Speculation has centred on MPs including former shadow cabinet ministers Chuka Umunna, Chris Leslie and Owen Smith.
They have remained tight-lipped about the situation and former leadership challenger Mr Smith said he was "not commenting" on the rumours.
There has been anger from some pro-EU Labour MPs at Mr Corbyn's refusal to throw the party's weight behind calls for a so-called People's Vote on Brexit.
Mr Corbyn refused to comment as he left his north London home on Monday morning.
Labour MP Stephen Kinnock told BBC Radio 4's The Westminster Hour on Sunday: "The talk has been going on so long that I say with great regret that, yes, there probably will be some kind of splintering.
"It just seems to have been in the rumour mill so long that it's unlikely that wouldn't be the outcome."
On Sunday morning, shadow chancellor John McDonnell said he did not see "any need for anybody to split from the party".
Mr McDonnell also revealed that Labour would "look at" a proposal put forward by backbenchers Peter Kyle and Phil Wilson to back a second Brexit referendum in the next round of votes on February 27.
Former Labour vice chairman Michael Dugher said at the weekend that he is intending to leave the party, saying he regards it as "institutionally anti-Semitic".
Mr Dugher, who was elected MP for Barnsley East in 2010 and left Parliament in May 2017, claimed the party he joined nearly three decades ago "no longer exists".
Manuel Cortes, general secretary of the TSSA transport union which backs a second EU referendum, said: "I'd urge anyone in our party thinking of bolting not to do so.
"Brexit, or any other issue, isn't an excuse for breaking away. Labour is the only show in town for creating a fairer Britain.
"Our voters need our MPs to be made of sterner stuff."