London Mayor Ken Livingstone faces a fresh investigation over remarks made to two wealthy businessmen.
Mr Livingstone is already fighting a one-month ban from office
He told brothers David and Simon Reuben to "go back to Iran and try their luck with the ayatollahs" in March.
Mr Livingstone had accused the pair of jeopardising the consortium behind Stratford's planned £4bn Olympic City, in which they hold a 50% stake.
If found guilty of bringing his office into disrepute, he could be suspended or asked to apologise.
'Back to Iran'
He is already appealing against a month-long suspension for likening a Jewish journalist to a Nazi concentration camp guard.
The mayor made his remarks to the Reuben brothers during a news conference at City Hall in central London.
He said: "If they're not happy here, they can go back to Iran and try their luck with the ayatollahs, if they don't like the planning regime or my approach."
The Reubens are not Iranian, but were born in India to parents of Iraqi-Jewish descent.
The Standards Board for England, the local government watchdog, has asked the Greater London Authority's monitoring officer to investigate the mayor's comments.
Once the inquiry is finished, the case is then referred to the GLA's standards committee, which has the power to suspend Mr Livingstone for up to three months.
A spokesman for the mayor said: "We are aware of developments and are not saying anything more at this stage."
The Commission for Racial Equality is also looking into whether Mr Livingstone's remarks breached race relations laws and compromised the GLA's duty to fight discrimination.