Power utility Eskom said on Monday afternoon that South Africans should start planning for load shedding to take place sometime this week.
This after the power utility earlier warned of a constrained national power supply - which it said was caused by protests and intimidation - for the first time since late June. Eskom put out similar warnings ahead of rotational load shedding in the past.
On Monday afternoon at 16:00 Eskom said in an update that customers "are advised to plan on the assumption that load shedding will take place".
"[Customers] are encouraged to check their load shedding schedules on the Eskom and their municipal website."
It did not say when it expected the rotational power outages to be implemented.
A month without load shedding
South Africa experienced several days of load shedding in mid-June. At the time, Eskom blamed the power outages on acts of intimidation and sabotage by workers who were locked in wage negotiations. Unions denied they were involved, however.
The wage negotiations are still on-going.
"The national grid is expected to be constrained this evening due to instability at several power stations due to acts of intimidation. Several power stations [are] now running at skeletal staff, a move that could compromise our ability to ensure security of power supply," wrote Eskom spokesperson Khulu Phasiwe in a tweet on Monday afternoon.
The power utility was also investigating why certain units had gone offline, Phasiwe said.
"A handful of power generating units, including two at Matla, one at Koeberg and Arnot, are currently offline. Investigations are continuing to determine the cause of these outages. A conveyor belt was cut at Matla power station in what management believes is an act of sabotage."
Phasiwe added that coal trucking at Majuba and Duvha power stations had stopped due to "acts of intimidation".
"This poses a threat to security of power supply," he said.
The National Union of Mineworkers, meanwhile, one three unions at the power utility, on Monday confirmed there had been disturbances at some power stations, attributing them to Eskom's position on bonuses.
"We have received reports about some form of protests at a few power stations. Workers are unhappy with Eskom position of insisting that there will not be paying bonuses this year," said NUM spokesperson Livhuwani Mammburu.
"The issue of bonuses is part of the workers' contracts' now Eskom wants to renege on that agreement. Their position is that the company cannot afford bonuses as it is struggling financially."
The NUM, the National Union of Metalworkers of South Africa (Numsa) and Solidarity are currently discussing the latest Eskom wage offer, a vast improvement from the no-increase position initially adopted by the cash-strapped power utility.
The state-owned power supplier recently reported a net loss of R2.3bn and total debt of R367bn. The company warned that its financial woes would get worse before stabilising.
Last week it secured a $2.5bn (about R33.3bn at the time) loan from the China Development Bank, which it said will be used for construction of Kusile power station.
A full-blown strike by Eskom workers is likely to cripple the electricity supply and cause outages across the country.