The National Union of Mineworkers (NUM) on Wednesday formally notified Eskom of its intention to go on strike next week over wages, a union spokesperson said.

"Today [Wednesday] we started mobilising our members for the strike," said NUM spokesperson Lesiba Seshoka.

The possibility of the industrial action being illegal because Eskom was an essential service "doesn't matter".

"We will cross that bridge when we get to it. We have already notified them of our intention to go on strike," said Seshoka.

"They cannot tie us to a tree and then tell us we can't do anything when abused because we cannot untie ourselves.

"We are going on strike and they cannot do anything about that."

Seshoka said Eskom's most recent offer was for an 8,5% wage increase and a R1 000 housing allowance. Unions have demanded a 9% increase and a R2 500 housing allowance.

Seshoka said the NUM would have been willing to compromise on the wage increase only if management had acceded to its housing allowance demand.

He said union leaders were busy with logistics on Wednesday to ready themselves for the strike.

Of the meeting Eskom said it was organising for Wednesday, Seshoka said: "We never planned to meet with them. Why would they organise meetings when we have rejected their offer and they have nothing new on the table?"

Eskom human resources director Bhabhalazi Bulunga insisted that "even if [the unions] notify us of the strike, it remains illegal. It's like telling someone you are going to murder them, that doesn't make the act legal."

He said NUM was risking committing itself to illegal action and getting its members arrested.

"We are an essential service, and therefore the security agencies will take over and arrest anyone engaging in illegal activities," said Bulunga.

He said that Eskom was unable to meet with Solidarity and the National Union of Metalworkers of SA (Numsa), its other unions on Wednesday.

"We were busy with internal meetings, trying to put contingency plans in place in light of the rumours of the strike.

"Besides, they are also still consulting their members, we did not want to push them," he said.

Numsa spokesperson Alex Mashilo said the union was still consulting its members on what action to take on Wednesday.

However, Solidarity said that it would not accept Eskom's latest wage and had delivered certain revisions for the power utility to consider.

"We need more time to discuss with our members. We believe there's still room for negotiations," said Solidarity's general secretary Flip Buys.

Buys said there were obstacles in the way of a settlement and that these had to be addressed for negotiations to be concluded.

Eskom had been given until Monday to respond to revisions, including a minimum service agreement, which the union said had to be in place before 2011 wage negotiations. Currently, there is no minimum service agreement meaning that workers can not go on a protected strike.

"Workers can not vent in the current situation," said the union's deputy general secretary Dirk Hermann.

The union also wanted an external audit within Eskom to determine the existing tensions between workers and management.

"We are experiencing real labour relations problems with Eskom... This break in trust of such a nature can not continue or else we will have this sort of dispute every year," he said.

"We want to know why and what is the problem within Eskom."

There was also a lot of frustration after it was reported that Eskom spent R12-million of World Cup tickets.