Alternative plans have been made to keep the lights on across the country as Eskom workers plan to embark on potentially disruptive pickets this week.
The power utility said on Tuesday it would "activate" its contingency measures in the case of industrial action.
It did not say what these measures were.
The uncertainty at Eskom follows the collapse of wage negotiations with organised labour, with the company saying it has no resources to hike wages in the face of union demands of 15% to 9%.
If the power utility gets its way, its 47,000 employees will receive no pay adjustments or improvements to other conditions of service such as housing allowances and leave.
Eskom is under pressure to deal with its excessive debt burden and its new management said it would focus on cutting costs as well as freezing posts, to ensure the survival of the power utility.
Old foes the National Union of Mineworkers (NUM) and the National Union of Metalworkers of SA (Numsa) put on a united front on Tuesday, detailing their fight-back plan.
Trade union Solidarity, which is also recognised at Eskom, last week declared a dispute over the failed wage negotiations.
Numsa and the NUM have followed suit, declaring a dispute of interest at the Commission for Conciliation, Mediation and Arbitration (CCMA).
"We will exhaust all options available to us legally before resorting to go on strike," said Numsa’s general secretary, Irvin Jim.
"We have scheduled pickets during lunchtime in different parts of the country where workers will demonstrate their disgust with Eskom for their provocative stance," he said.
Eskom employees are considered "essential services" and cannot embark on industrial action. Disputes are usually referred to the CCMA for conciliation and arbitration.
The two unions called on the government to do "everything" to ensure the cash-strapped power utility was resourced to increase employees’ wages or "the lights will switch off".
The unions’ leaders did not rule out a Treasury-sponsored "bailout" in its call for government intervention.
Requests for urgent meetings with the Eskom board, President Cyril Ramaphosa and Energy Minister Jeff Radebe would be made to resolve the impasse speedily, said Jim.
Eskom said while it "sympathised" with its employees, the difficult financial situation at the company had motivated its decision to offer no salary increases in 2018.
Eskom has debt amounting to R367bn.
The unions dismissed the power utility’s explanation on why wage increases could not be effected.
The NUM’s general secretary, David Sipunzi, said corruption at the entity and the implementation of the independent power producer programme were just some of the reasons the utility found itself in the red.
Meanwhile, the National Energy Regulator of SA has confirmed it has received notice of Eskom’s intention to take its decision on revenue requirement for the 2018-19 financial year for judicial review.
The national regulator approved an average price increase of 5.23% after Eskom had applied for 19.9%.