Police say they have opened two cases of intimidation related to the unlawful strikes at Eskom, which the power utility has blamed for Stage 6 load-shedding. 

"One was registered at Belfast Police Station while the other was registered at Hendrina Police Station. Both matters are still under investigation," said police spokesperson Colonel Athlenda Mathe.

"The SAPS has deployed its Public Order Police as police continue to closely monitor the situation at all Eskom sites that have been affected by the strike."

Eskom's leadership and Minister of Public Enterprises, Pravin Gordhan, have said that intimidation of employees has contributed to significant staff shortages at power plants.

On Tuesday, the minister said that houses and cars of some managers had been targeted by petrol bombs. "In many power stations up to 90% of the staff could not attend to their duties."

While some employees started to return to work from Wednesday, Eskom has said that absenteeism and intimidation of working employees were still "rife".

"This has made it difficult to conduct routine maintenance and other operational requirements, which will further impact the reliability of generation units," the utility said on Thursday. 

Eskom management and unions are set to return to the Central Bargaining Forum on Friday to resume wage talks.