Four striking truck drivers were injured in downtown Johannesburg on Monday after the police fired rubber bullets at them, SABC radio news reported.
An SABC journalist on the scene said some of the striking workers had assaulted a truck driver who was not taking part in the labour action.
The police intervened and fired rubber bullets at the striking drivers, injuring four people.
The disgruntled road freight workers in Gauteng had gathered at the Mary Fitzgerald square in Newtown, where they were planning to hold discussion rallies ahead of Wednesday's strike action over wages.
SA Transport and Allied Workers Union (Satawu) president June Dube told Sapa workers were merely gathering and would not be marching on Monday.
Workers embarked on a go-slow at various working stations on Sunday, demanding a 20 percent increase over two years. The Road Freight Employers Association (RFEA) was offering 15 percent.
Dube told Sapa workers would be meeting with the employer on Tuesday, which was confirmed by the association's labour relations manager, Magretia Brown-Engelbrecht.
The union warned that the road freight industry will be brought to a standstill as about 65000 members would be joining the strike.
The wage talks between the unions and RFEA have deadlocked since December and the unions were issued with a strike certificate by the Commission for Conciliation, Mediation and Arbitration.
In 2009, Satawu and RFEA signed an agreement, which included an 11 percent wage increase for all road freight industry workers across the board after workers embarked on a seven-day strike. - Sapa