Eskom is under investigation by the National Electricity Regulator (Nersa), SABC news reported on Tuesday.

The investigation was prompted by January's unexpected load shedding, after Eskom's unplanned maintenance of its generators, the report said.

Stiff penalties could be on the cards if the power utility transgressed its licence conditions.

The conditions include maintenance of schedules; code of practice for electricity metering; standards of service and quality of service.

Eskom is due to explain itself before the Nersa Board next week.

Its capacity, coal reserves, and unplanned maintenance are some of the issues that will be probed.

If licence conditions were transgressed, Eskom will have a lot to answer for ... "even a R2-million fine per day", said Nersa's executive manager Mbulelo Nceteza.

Nersa will also be looking at public submissions on Eskom's application to hike tariffs by 53 percent. Tuesday was the cut-off for written submissions. Nersa would make its decision known on June 6, SABC reported.