Workers of Nigeria's state-run power firm on Wednesday protested the deployment of armed troops to their offices across the country in the wake of an order by their union to launch a pay strike.

Government deployed the troops on Monday to the offices and installations of the Power Holding Company of Nigeria (PHCN), a move which Power Minister Barth Nnaji said was aimed at protecting these facilities.

He said the secretary general of the National Union of Electricity Employees, Joe Ajaero, had ordered electricity workers to embark on the strike from Monday to protest non-payment of 50 percent salary increase, government planned reform of the electric power sector, including privatisation of the company.

Some PHCN workers Wednesday protested the presence of the soldiers around their offices.

"We are not going to work with soldiers around our premises. You cannot intimidate us with soldiers," Mbang Mbukubes, a spokesman of the workers, said on local Channels television.

The television showed footage of some placard-carrying PHCN workers as well as soldiers around the offices and facilities of the power firm.

"It is improper for any person to reject, in the name of trade unionism, the presence of military men and women in power facilities in which the nation has made huge investments over the decades," the minister said in a statement.

The strike order is "illegal" and constituted a "grave danger to national security and development", he said in the statement on Wednesday.

The minister also said that Nigerian law prohibited PHCN workers from going on strike "because they provide an essential service".

PHCN spokeswoman Efuru Igbo told AFP "the soldiers are guiding us. There is a security challenge in the country at this moment."

An Islamist sect known as Boko Haram has carried out scores of attacks in Nigeria, including an August suicide bombing of UN headquarters in Abuja which killed at least 24 people.

It also claimed a bomb blast in the national police headquarters car park in the capital in June that killed at least two people.

Power supply in Nigeria, Africa's largest oil producer is woefully inadequate. It currently produces around 4,000 megawatts for a population of more than 160 million.