Eskom, which has struggled to meet power demand in Africa's most industrialized nation for over a decade, has been implementing "Stage 2" rotational outages since the start of the week.
But it will increase the severity of the outages to "Stage 4," requiring up to 4,000 megawatts (MW) of capacity to be shed from the national grid, from 1100 local time until midnight (from 0900 to 2200 GMT) on Friday.
Stage 4 outages will also be implemented from 0500 local time until midnight on Saturday and Sunday.
"While exploring possible solutions to unlock the deadlock with the unions, Eskom appeals to its labour partners and striking employees to embrace the higher purpose of putting the people of South Africa first," Eskom said in a statement.
Eskom said earlier that the protests had included incidents of intimidation of working employees and blockades on roads leading to power stations. The company has asked police to restore order.
The negotiations with trade unions including the National Union of Metalworkers of South Africa broke down on Tuesday. Eskom's wage talks have turned fraught in the past, leading to similar protests which hampered operations.
The loss-making utility, saddled with a huge debt pile approaching 400 billion rand ($25.12 billion), is trying to contain costs as part of turnaround efforts under Chief Executive Andre de Ruyter.
