The energy regulator has given Eskom the go ahead to adjust rates above the 8% already granted.
Eskom says the power constraints have improved significantly this weekend.
Cosatu said the poor and struggling small businesses will still have to tighten their belts.
Numsa will lodge an application against the implementation of Eskom's proposed 16% tariff hike.
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.