A group of London Labour party members are backing moves to readmit Ken Livingstone to the party.
Mr Livingstone was expelled for running as an independent in 2000
On Thursday, Labour mayoral candidate Nicky Gavron said the best way to reunite the party's vote in London was to combine both campaigns.
Labour's ruling board is expected to decide next week whether to readmit Mr Livingstone to the party early.
He had been expelled for five years for running against Labour in the 2000 mayoral poll.
In an open letter to the Independent London Assembly members, a London MEP, two MPs
and three union officials said Ms Gavron's proposal was "a welcome step".
The letter adds: "Labour needs a sizeable group on the London Assembly in order to continue investment in public services in the capital.
National Executive meeting
"London Labour Party members want a united campaign in order to maximise Labour's vote and promote Labour's values.
"Mr Livingstone's readmission would be the strongest basis for achieving unity in London."
Labour's London regional board may discuss Mr Livingstone's position when it meets on Monday, ahead of the party's National Executive Committee meeting on Tuesday.
Earlier, Ms Gavron said: "During the last few months I have listened
intently to the views and concerns of party members and supporters at every
"My absolute priority is to reunite the Labour vote in London.
"The best way
to achieve this unity is to combine the existing strengths of both our campaigns
and for Ken Livingstone and myself to work together for the good of Labour and
Prime Minister Tony Blair is thought to want Mr Livingstone back into the Labour fold amid fears that Labour's official candidate could be pushed into fourth place in next year's election.
But Chancellor Gordon Brown and Deputy Prime Minister John Prescott are among other ministers believed to be opposed to the move.