Mr Johnson has criticised the police over the Damian Green affair
London Mayor Boris Johnson's involvement in the Damian Green affair has become the subject of a formal complaint by Labour politicians.
Mr Johnson has admitted he contacted Tory immigration spokesman Mr Green after recent arrest by Met police.
Labour assembly member John Biggs told the BBC Mr Johnson had "jeopardised the integrity" of the Metropolitan Police Authority (MPA), which he chairs.
He said London's Labour leader had complained to the MPA chief executive.
Mr Biggs told the BBC's Politics Show he believed Mr Johnson had "damaged his office".
As chairman of the MPA, Mr Johnson had been briefed on the arrest by the Met but the mayor told the assembly last week that he felt he did nothing wrong in contacting Mr Green.
Mr Green was arrested and held for nine hours on 27 November on suspicion of conspiring to commit misconduct in public office and on suspicion of aiding and abetting misconduct in public office. He denies any wrongdoing.
Mr Biggs said London's Labour leader Len Duvall had formally complained to the MPA's chief executive Catherine Crawford, alleging that Mr Johnson has brought the authority into "disrepute".
"He's told us he had a personal conversation with Damian Green," Mr Biggs said.
"Following a confidential briefing from the police commissioner, he has to be extraordinarily careful what he says to other people and the good advice is to keep clear of speaking to people who might be suspects of an investigation."
Mr Biggs said Mr Johnson is in a clear position of conflict.
"There is a conflict between his public role as a politician and his rather more formal and rather private role as chair of the police authority."
The letter from Mr Duvall will automatically prompt an internal investigation and could end with the mayor facing a formal inquiry by the Standards Board for England.
In such a case, the mayor could be subjected to a suspension or even removed from public office if he is found to have abused his position.
Former mayor Ken Livingstone was suspended from his office in 2006 by the Standards Board over a complaint that he had compared an Evening Standard journalist, who was Jewish, to a concentration camp guard. That decision was overturned on appeal.
Mr Johnson has steadfastly defended his involvement in the ongoing inquiry and said he did not believe any charges or a prosecution would result from the investigation of his former Commons colleague.
A spokesman for his office said the mayor stood by his actions.