Hundreds of union members picketed outside the headquarters of Eskom on Thursday because of a wage dispute which has hurt the cash-strapped South African power utility's ability to deliver electricity to Africa's most industrialised economy.
Labour unions, angered by Eskom's failure to raise salaries as it embarks on a cost-cutting drive, have threatened a "total shutdown" of Eskom's operations if the utility does not cede to their demands to raise salaries by 15%.
The pickets come a day after protests at around ten Eskom power plants forced the state-owned firm to switch off some generating units because trucks carrying coal and busses ferrying staff were blocked by picketing workers from entering the plants.
Eskom's spokesperson Khulu Phasiwe said some units at power stations were still switched off on Thursday but that the firm had activated contingency plans to ensure that a sufficient amount of power was being generated.
Police were on hand at power stations and the firm's Megawatt Park headquarters to protect staff and Eskom equipment, he added.
The National Union of Mineworkers (NUM) and National Union of Metalworkers of South Africa (Numsa), who say they represent more than 20 000 out of a total of 47 000 Eskom employees, say thousands of their members will march to Megawatt Park later on Thursday to keep up the pressure in the wage negotiations.
Stabilising the finances of Eskom, which produces more than 90% of South Africa's power, is a priority for President Cyril Ramaphosa as he looks to rekindle growth after nine years of stagnation under his predecessor, Jacob Zuma.
Ramaphosa oversaw the appointment of a new board and chief executive at Eskom in a bid to clean up governance and set the firm on a firmer financial footing.
Later on Thursday, South Africa's energy regulator Nersa will announce its decision on whether Eskom should be allowed to recover more than R60-billion ($4.55-billion) of costs via higher electricity tariffs.