Eskom, in a statement, said, "These protests included incidents of intimidation of working employees and blockading of roads leading to power stations and other facilities, inhibiting the free flow of personnel and commodities required for the generation of electricity."
"Should these criminal acts of intimidation persist or spread, this would increase the risk of ... load shedding at higher stages," it said.
The power system is already under considerable pressure, with Stage 2 rotational cuts underway, requiring up to 2,000MW to be shed from the national grid.
Eskom said it had been making extensive use of emergency generation reserves, which were depleting faster than could be replenished.
On Tuesday, salary negotiations with trade unions, including the National Union of Metalworkers of South Africa, broke down after multiple rounds of talks.
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