The energy regulator has given Eskom the go ahead to adjust rates above the 8% already granted.
Numsa has called on its members to join a planned night vigil and a picket outside Nersa offices.
Eskom says cutting its maintenance budget is out of the question.
Eskom has ruled out suggestions that it proposed an inflation-linked electricity tariff hike.
Eskom says the electricity tariff hike is necessary for infrastructure maintenance and growth.
Mines have warned they’ll be forced to lay off workers if Eskom gets its 16% electricity tariff hike.