Power utility Eskom has been granted an urgent court interdict preventing the trade unions and their members from participating in industrial action from Wednesday onwards.
Eskom said late on Tuesday evening that it had been granted the urgent interdict.
The National Union of Mineworkers (NUM) said 16 000 Eskom workers planned to go on strike from Wednesday this week.
Some workers reportedly started striking at Eskom plants on Tuesday.
Since the workers would be striking at power stations, the industrial action was seen as threatening security of supply.
"Eskom is an essential service and employees of an organization classified as such are prohibited from taking part in industrial action. Engaging in any such action would be considered unlawful," Eskom said in a statement.
But the utility said if a strike did take place, it has contingency plans to ensure security of supply.
Eskom said it held discussions with NUM leadership on May 21 and 23, where both parties committed to working together within the Central Bargaining process, which is scheduled to meet on Wednesday and Thursday this week.