Kenya Power has been involved in a protracted dispute with the Kenya Electrical Trade and Allied Workers Union (KETAWU), which claims that more than a third of the workers are on casual terms, in violation of the country's labour law.

The union called off another strike last September, saying they had secured agreement over the issue.

Ernest Nadome, secretary general of the union, told Reuters by phone that 6,000 workers had downed tools after Kenya Power failed to honour this year's collective bargaining agreement.

"We are demanding our rights. We will not be cowed by threats, "Nadome said.

Kenya Power, on the other hand, said 75 percent of the staff reported to work, while those who did not report feared for their safety. "About 4,500 reported to work.

But we will carry out a roll call at 2 pm (1100 GMT)," said Migwi Theuri, communication manager at Kenya Power.

The firm said in a separate statement it had issued warning letters to another group of workers at the coastal city of Mombasa, who stayed away from work on Friday.

"Staff not at the work places will be considered to have absconded duty and will also face disciplinary action," the company said in a statement, adding the union should return to the negotiating table.

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