Johannesburg - Members of the National Union of Mineworkers (Num) handed over a memorandum of demands to Eskom executives in Durban on Saturday.
This was after its members marched to demand improved conditions of employment and decent wages.
The letter was addressed to Eskom board chairperson Zola Tsotsi and chief executive Brian Dames, and requested action on a number of issues of concern to the workers.
In the letter, Num said its members had lost confidence in Eskom executives as they "have paid themselves astronomical increases".
The union was opposed to the company implementing its offered 7% increase "unilaterally".
On Thursday, Eskom human resource executive Bhabhalazi Bulunga said the increase would be reflected on the September payroll. A systems upgrade at the company meant that if it were not implemented in September, workers would have to wait until November for the increase to be reflected on their pay cheques.
Num was also unhappy about the "significantly increased wage gap" between top executives and ordinary workers.
Num, the National Union of Metalworkers of SA (Numsa) and Solidarity were in wage talks with Eskom, which deadlocked on Wednesday.
The unions demanded a 13% increment, but Eskom's last offer was 7%.
The march was part of "big wars to come" with the parastatal electricity supplier if it did not concede to the unions demands, spokesperson Job Matsepe said.