Strikes by petrol attendants and vehicle industry workers entered its third week on Monday, Numsa treasurer Mphumzi Maqungo said.
"The strike will be tougher as it is affecting the entire auto sector," said Maqungo.
The National Union of Metalworkers of South Africa met with the Retail Motor Industry (RMI) for wage talks last week, but no agreement was reached.
"We met last week with the hope that we will be getting a revised offer, but they did not come to the party.
"On the 25th, [Wednesday], we are meeting again and we are hoping that we will be given an offer we can consider," said Maqungo.
RMI chief executive Jakkie Olivier denied at the weekend allegations by the Cosatu that they were unnecessarily stalling negotiations.
He was optimistic that an agreement would be reached soon.
"Though we have not reached an agreement with labour, there are talks … to reach a settlement that will suit all parties," Olivier said after talks last week.
Around 70 000 workers from across the country were taking part in the strike, said Maqungo.
Workers downed tools on September 9 with Numsa demanding a double digit percentage increase.
They want a R30 an hour across the board increase by 2016 on actual rates of pay in all sectors and divisions for workers earning above R6 000 a month, among other demands.
The union has rejected a revised wage offer of 7.5%. – Sapa