"Production has stopped at five mines. Exxaro is engaging with unions and managing the situation to bring operations to normal as soon as possible," it said on Monday.
Wildcat strikes are taking place at coal miner Exxaro's Matla, Arnot, Grootegeluk, Leeuwpan and Inyanda mines.
On Thursday, Exxaro announced unprotected strikes at Matla and Arnot in Mpumalanga.
The strike at Grootegeluk, in Limpopo, started on Friday and involved a range of grievances.
"The strikes are related to different issues at the mines. The Matla and Arnot strikes started on March 5 and are related to non-payment of performance bonuses due to the operations having not achieved their performance targets."
The strike at Leeuwpan started on Saturday, while the Inyanda strike started on Monday.
Contingency plans were in place to supply customers, the company said.
"Employees have been regularly kept informed of performance levels and bonus payments. The mines have adequate stock days of supply on hand for their respective power stations." – Sapa