South African police have used rubber bullets and water cannon on striking public sector workers as the demonstrators tried to block a main road in Soweto.
More than one million teachers, healthcare workers and others have begun an indefinite stoppage claiming higher wages.
The strike has disrupted hospitals and shut schools across the country.
The flashpoint occurred when crowds brought traffic to a halt near a hospital, preventing patients from entering.
No major injuries were reported. Police said they had to use minimum force to disperse the crowd.
South Africa’s ANC government has offered a seven percent pay rise, and said it cannot afford union demands for 8.6 percent – double the inflation rate.
It has also offered to raise the monthly housing allowance for civil servants to the equivalent of 75 euros, but the unions are holding out for more than 100.
Mid-level civil servants reportedly earn about 40 percent more than the average worker.
The finance minister said he did not believe a protracted strike would seriously affect the economy.