Eskom, which generates more than 95 percent of the country’s electricity, has blamed the power shortage on industrial action and “sabotage”.

It said on Friday it had commenced “load shedding” — a term for regularly-scheduled power cuts that reduce demand for energy.

“This is due to the impact of the current illegal protest action by some Eskom employees at various sites over wage increases,” it said.

On Thursday, the company announced electricity generation was being “constrained… (due to) acts of sabotage and intimidation.”

The workers have rejected any blame.

“Eskom has no evidence to back up allegations that our members are responsible for sabotaging power supply,” said Phakamile Hlubi-Majola, spokeswoman for the National Union of Metalworkers of South Africa (NUMSA).

Eskom’s workers are demanding a pay rise of up to 15 percent, but the company has ruled out any increase, saying it has liquidity problems. On Thursday, employees went on strike and began to picket power plants.

The government of Cyril Ramaphosa is reining in on loss-making state-owned companies, some of which have been at the centre of corruption scandals under his predecessor Jacob Zuma, who was forced to resign in February.

Eskom first introduced load-shedding in 2008, affecting commerce and industry while also plunging many neighbourhoods into darkness.

The highly unpopular measure, which continued until 2015, was long blamed for hobbling economic growth. In 2006, the economy expanded by 5.6 percent, but it fell back sharply in subsequent years.

The most recent official statistics show that South Africa’s gross domestic product (GDP) contracted by 2.2 percent from January to March compared with the preceding three months, the sharpest contraction in nearly a decade.