NUM general secretary David Sipunzi said on Wednesday that the strike would involve all its members employed at the utility without offering a timetable.
The union has about 15 000 members at Eskom, close to a third of Eskom’s workforce.
The union said the power station closures would translate into 10 000 direct job losses and as many as 40 000 around the stations and at the coal mines that supply them.
Read also: Eskom wants to mothball five plants
Eskom has said that its workers cannot strike because it provides essential services. Coal is used to generate more than 90 percent of South Africa’s power supply and job cuts are a sensitive issue in a country where the unemployment rate is almost 27 percent.