The London Assembly's Liberal Democrats have claimed the mayor has set aside £100,000 to fight an appeal over a rejected Nelson Mandela statue.
The statue has been rejected by Westminster Council
Ken Livingstone wants the figure for Trafalgar Square but the plans have been thrown out by Westminster Council.
He is appealing to the deputy prime minister's office but the Lib Dems say it is a waste of public money.
The mayor's office declined to comment on the £100,000 figure, which Lib Dems said was revealed in expenditure forms.
The mayor said said an appeal was the only course of action left, and urged the Lib Dems to back the idea.
'Bury the hatchet'
But Dee Doocey, the Liberal Democrats' London Assembly culture spokesperson, said: "It is ironic that the statue of the man who embodied freedom is now bogged down in so much bureaucracy.
"Thousands of pounds of taxpayers money is set to be wasted in these costly arguments.
"It is time that Westminster Council and the mayor buried the hatchet and found a way to resolve their differences so that London can proudly recognise the work of Dr Mandela."
But Mr Livingstone said: "By opposing this appeal Dee Doocey and her colleagues have set themselves against the only avenue left to us to get it [the statue] erected.
"I am sorry that the Lib Dems on the London Assembly have decided to back Westminster's rejection of the statue of Nelson Mandela on the north terrace of Trafalgar Square by coming out against the appeal.
"They have proved themselves to be fair-weather friends of this statue. "
Westminster Council said in July that it rejected plans for the 9ft tribute to the former South African president because it was not in keeping with the "open nature" of the terrace.
It says the statue should go outside South Africa House - the scene of many anti-apartheid protests in the square.