Cosatu will take to the highways in cars on Thursday to protest against e-tolling in Gauteng, it said on Wednesday.
"We won't be marching and demonstrating with our feet this time; we will be demonstrating with our wheels," Congress of SA Trade Unions (Cosatu) Gauteng chairman Phutas Tseki told reporters in Johannesburg.
"We will be driving slowly."
Tseki said this was not a strike and that workers would be at their posts on Thursday.
Cosatu leaders, full-time shop stewards, and leaders of Cosatu affiliates were expected to participate.
"We will do this for almost seven hours," Tseki said.
There would be two campaigns - one in Ekurhuleni and one in Johannesburg.
Motorists would meet at 6am on the corner of Black Reef and Masakane roads in Ekurhuleni and on Jorissen Street in Johannesburg. The protest was expected to start at 8am.
The two protests would take place on some of Johannesburg's busiest highways - the N1, M2, M1, N3, N12, R24, and R21.
Tseki said 100 cars a route were expected.
Cosatu Gauteng secretary Dumisani Dakile urged motorists who joined the protest to drive with their car lights and hazards on. Some cars would also have banners.
"This is the first time we [are] marching on the freeways with cars," said Dakile.
"In February, we will push the campaign to the next level. This is the beginning, next time we will close the roads for 24 hours and if government doesn't listen we might close them for a week," he said.