Two former Cabinet ministers have written to Labour MPs calling for a secret ballot on the party's leadership.
Geoff Hoon and Patricia Hewitt's email does not call for Gordon Brown to resign, but says the issue must be resolved before the general election, which must be called by June 5.
The party leader is elected by the unions, the constituency Labour parties and MPs and MEPs, so it is unclear what effect a secret poll of MPs would mean for Brown's leadership.
In their email Hoon, a former defence secretary and Hewitt, former health secretary, both seen as supporters of Tony Blair, claimed the parliamentary Labour party is "deeply divided over the question of the leadership".
They called for a secret ballot as "the only way to resolve this issue" and such a vote "could be done quickly and with minimum disruption to the work of MPs and the government".
Hoon and Hewitt claim that Brown supporters should be in favour of a vote.
"Equally those who want change, should they lose such a vote, would be expected by the majority of the PLP (Parliamentary Labour Party) to devote all of their efforts to winning the election.
"The implications of such a vote would be clear – everyone would be bound to support the result."
Hoon, a former chief whip, told the BBC that he has not spoken to any members of the cabinet about the email.
He said colleagues had spoken to him over the Christmas break and there is concern the party is not getting its message across.
If a challenge to the prime minister is to succeed it would need support from senior members of the party.
Tony Lloyd, the chairman of the PLP, told the BBC:
"Geoff Hoon has very little support and that's the real issue for the Parliamentary Labour Party - what we want is for Gordon Brown to ignore this."
Danny Alexander, chief-of-staff to Lib Dem leader Nick Clegg, said: "Labour has given up any hope of winning this election and given up on governing the country. Labour MPs are now in a desperate scrabble to save their own seats and minimise their defeat."
Tory chairman Eric Pickles said Gordon Brown is "injured" and should call a general election.
Dods Parliamentary Communications Ltd