Johannesburg - Johannesburg mayor Parks Tau issued a strong warning on Friday to employees involved in turning off power at sub-stations around the city.
"The process of laying criminal charges has been undertaken," Tau told reporters.
He said the labour relations process had to be respected. However a situation where residents were deprived of electricity could not be allowed.
He said the matter was being investigated and certain people had been identified.
Before the briefing Tau met with City Power management to receive an update about the restoration of electricity in some parts of Gauteng.
This followed power disruptions in parts of the West Rand and northern Johannesburg after a few hundred City Power staff downed tools on Wednesday afternoon.
City Power said the strike was not union-led.
The workers were unhappy about a new shift system the power distributor was implementing.
It was believed that striking workers had sabotaged the infrastructure causing the widespread blackouts, which impacted on traffic flow and affected some businesses' operations.
Earlier on Friday power was fully restored to areas including Houghton and Melville by noon, while other parts of Johannesburg could be left in the dark over the weekend, City Power said.
The electricity supply was also reconnected in Auckland Park, Kew, and Bramley, the power distributor said in a statement.