Johannesburg - Unprotected strikes have stopped production at two Exxaro mines in Mpumalanga, the company said on Thursday.
The strikes at its Matla and Arnot coal mines began on Tuesday, said spokesperson Hilton Atkinson.
"The strikes are related to non-payment of performance bonuses due to the operations having not achieved their performance targets."
He said employees were regularly informed of performance levels and bonus payments.
"Exxaro is managing the situation to bring operations to normality as soon as possible and is engaging with the unions."
Atkinson said the mines had introduced contingency plans and at this stage there was a sufficient supply of coal to maintain the Matla and Arnot power stations.
"The Matla mine has 19 days' supply available and the Matla power station has two days' supply on hand. At Arnot there is no risk to supply of coal."
He said Exxaro would continue to work closely with power utility Eskom to ensure coal supplies.
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