An international trade union has condemned the disappearance of Iranian union leader Mansour Osanlou, who has reportedly been abducted in Tehran.
Mr Osanlou was previously detained in Tehran's Evin prison
Mr Osanlou's wife told the BBC her husband was pulled from a bus by unidentified men on Tuesday evening.
The International Transport Workers' Federation (ITF) has written to Iran's president to protest.
Mr Osanlou, head of Tehran's transport workers' union, spent most of 2006 in prison for running a strike in 2005.
As the director of the Union of Workers of the Tehran and Suburbs Bus Company, Mr Osanlou was first detained in December 2005 for organising a walk-out by bus drivers.
The drivers then planned another strike in January 2006 in response to his detention and to demand recognition of their trade union activities.
The Iranian government responded by pre-emptively detaining hundreds of drivers, including several union organisers.
All were later released, but Mr Osanlou was detained in Tehran's Evin prison for several months before being freed on bail.
His union is not recognised by the Iranian government, but it is the first independent Iranian trade unions to be affiliated to an international organisation, says the BBC's Pam O'Toole.
Mr Osanlou received a standing ovation when he spoke at a recent conference in Europe.
'Bullies and thugs'
The ITF said there was strong reason to believe Mr Osanlou was being held by the Iranian authorities.
The organisation's Secretary General, David Cockroft, says Mr Osanlou has frequently been badly treated by Iranian authorities.
"He's been imprisoned about three times now. He has been beaten up on arrest, [and] he has been the subject of harassment by the security apparatus inside Iran simply for being the president of one of the first independent genuine trade unions which have been established in Iran.
"All of us are behind him now and demand his release and the reining in of the bullies and thugs who are hounding him."
Iran has made no comment about Mr Osanlou's disappearance.