Mansour Osanlou, the leader of Tehran's municipal bus service union, was reportedly assaulted by an inmate in an Iranian prison, RFE/RL's Radio Farda reports.
The trade unionist was not injured in the attack, which occurred at Gohardasht prison in Karaj, west of Tehran, on February 22. Osanlou was arrested in July 2007 after being abducted on the street by security forces.
He is serving a five-year prison term for what authorities say was acting against "national security." He had been detained several times between 2005-2007.
Canadian-based labor activist Mehdi Kouhestaninejad told RFE/RL that Osanlou has been persecuted in prison by fellow inmates on several occasions.
But he said prison guards "turn a blind eye to these incidents and no committee is assigned to investigate them."
Kouhestaninejad added that authorities are trying to intimidate labor activists by arresting, detaining, and firing them. In recent weeks Iranian trade unions have issued statements condemning the crackdown on labor activists and demanding their release from prison.
The crackdown follows labor protests throughout the country in recent months, many focused on the problem of many months of unpaid salaries.