The National Union of Mineworkers says it will march to the ANC headquarters at Luthuli House on March 30 to protest the unbundling of Eskom.
This march will precede a planned "total shutdown" on May 3 leading up to the national general elections on May 8.
The decision was made at a NUM shopstewards council meeting on Tuesday in Midrand. The NUM, one of three recognised unions at Eskom, had previously announced its plans to march to Luthuli House but had not confirmed a date.
The union has criticised the unbundling of Eskom, announced by President Cyril Ramaphosa during his State of the Nation Address in February.
"So far, there is no guarantee or a solid commitment that signals there would not be retrenchments during the unbundling process. It is widely believed that the move will result in many job losses," NUM said on Tuesday.
"Secondly, the board of Eskom has totally failed in their duties to develop a turn-around strategy towards the improvement of Eskom's performance."