Stage 4 load shedding is due to continue until Wednesday.
In a statement, Eskom said unlawful industrial action at various Eskom power stations has affected planned maintenance and repairs. At some stations, the full complement of workers did not report for duty.
"Eskom regrets to inform the public that stage 4 load shedding is anticipated to continue from 5am on Monday morning until midnight at least until Wednesday. This is due to unlawful and unprotected labour action at a number of power stations, which has caused delays in carrying out planned maintenance and repairs," it said.
Eskom said as a result of this, unplanned generation losses have not been reduced as planned, which has compelled Eskom to continue taking precautionary measures to conserve generation capacity and safeguard plants from damage.
"There is a possibility that the stage of load shedding may have to change at short notice, depending on the state of the plant and the availability of labour," said the power utility.
Protracted strike action may lead to further damage and prolonged delays to returning units to service, which would compound an already constrained power system.
"We currently have 3 894MW on planned maintenance, while another 15 472MW of capacity is unavailable due to breakdowns. In addition to this, a further 600MW is unavailable due to a line fault in Mozambique, which is currently experienced by the Hydroelectrica de Cahora Bassa (HCB).
"Eskom wishes to pay tribute and thank those many loyal and dedicated employees who keep going beyond the call of duty to help to keep the lights on."
Eskom increased load shedding from stage 2 to stage 4 on Friday.