Johannesburg - The wage offer made to striking road freight workers was increased to 8% across the board after 17:00 on Wednesday, the SA Transport and Allied Workers Union (Satawu) said.
"The employers have just increased the offer by 0.5% but that is ridiculous," spokesperson Zenzo Mahlangu told Sapa.
"We are not on strike for just 0.5 - we will not accept it."
He said negotiations with the Road Freight Employers Association (RFEA) would continue until 20:00 on Wednesday.
"I hope they will shift with upward figures soon... otherwise we won't stop striking," said Mahlangu.
Initially, the RFEA offered an increase of 7.5% across the board for 2011 and a further 7.5% increase for 2012.
Four unions involved in the strike - the Transport and Allied Workers Union of SA, the Professional Transport Workers Union, Satawu, and the Motor Transport Workers Union - are demanding a 20% increase allocated over a two-year period, for example 10% in 2011 and 10% in 2012.
The disruptive countrywide strike, in which several people were injured, entered its third day on Wednesday.
About 65 000 workers were participating in it.
Union members earlier marched through central Johannesburg and delivered a memorandum to the RFEA.
Police Minister Nathi Mthethwa was prompted to issue a warning to protestors that acts of intimidation and violence would not be tolerated. It came in the wake of acts of intimidation and the destruction of property allegedly by striking truck drivers.
Four people were seriously injured after a truck driver, in an attempt to avoid being attacked by striking workers, veered into the taxi they were travelling in. Other trucks were burned and looted.
Eyewitness News reported that trucks at the Cleveland and Kaalfontein train stations were being stoned as well as trucks along Ontdekkers Road.