Traffic authority warns motorists that members of the SA Transport and Allied Workers Union (Satawu) are set to march in downtown Johannesburg to demand better wages.

"All motorists are advised to avoid the affected route," said Johannesburg metro police spokesman Wayne Minnaar on Wednesday morning.

The protest will start on the corner of Miriam Makeba and Jeppe streets at around 10am.

"It will then proceed up Miriam Makeba, right into Carr street, left onto the Nelson Mandela bridge, over the bridge and up to 29 De Korte street," said Minnaar.

"Satawu members will be protesting from 10am up until 2pm."

On Monday, four protesters were injured in Johannesburg after police fired rubber bullets in the city centre at protesters who had smashed the windows of trucks and pulled drivers out of their vehicles.

The unions involved in the wage dispute are the PTWU, Satawu, the Motor Transport Workers Union (MTWU) and the Transport and Allied Workers Union of SA (Tawusa).

The workers are demanding an increase of 20 percent over the next two years and the banning of labour brokers.

The Road Freight Employers Association (RFEA) was offering an increase of 7.5 percent across the board for 2011 and a further 7.5 percent increase for 2012.

The wage talks between the unions and RFEA deadlocked in December.

Truck drivers started a go-slow on Sunday, sparking fears of fuel shortages and cash running out at ATMs.