Mehdi Karroubi, a presidential candidate and former Speaker of the Iranian regimes Majlis (parliament), was speaking to the gathering Wednesday evening when a crowd of some 30 people charged at him on the platform.
According to a hard-line state-run news agency Karroubi was forced to stop speaking and had to leave the area.
On May 01, another presidential candidate, ex-President Ali Akbar Hashemi Rafsanjani was forced to call off his scheduled speech at a May Day gathering in Tehran.
Eye witnesses said that the packed Azadi Stadium was the scene of angry anti-government protests, adding that some 20,000 workers had gathered in and around the 12,000-seat stadium to mark May Day and chants of The Majlis (parliament) betrays us, the leaders support them could be heard throughout the crowd.
The event was originally organised by the government, however it soon became the scene of hostilities towards the regimes clerical rulers. One eye witnesses said that the crowd grew particularly incensed upon hearing the news that Rafsanjani was using the labourers event as part of an election stunt.