Civil servants have been in dispute with management since last year

The escalation is part of the continuing pay dispute between the union Nipsa and the government.

The government has imposed a pay package which will add 3.67% to the wage bill of the Northern Ireland Civil Service.

However, union officials say that was part of a pre-agreed increment and takes no account of the rise in the cost of living.

Staff at three jobs and benefits offices will be on strike this week.

Nipsa said up to 300 workers from the offices at Lisnagelvin and Foyle in Londonderry and at Newtownabbey in County Antrim would be taking part in action.

The Lisnagelvin and Foyle offices closed on Monday and the Newtownabbey office was shut down from Tuesday, said Nipsa.

Members have been supporting this industrial action campaign for over three months and hundreds of members have been involved in rolling selective strike action John Corey Nipsa General Secretary

It said six of its members at the Newtownabbey were suspended from duty last week.

They were suspended without pay after they refused to go on a training course.

The Department of Employment and Learning said the staff at the Newtownabbey branch were in breach of contract.

'Minimise the impact'

Social security operations in Lurgan in County Armagh, Newry in County Down and Derry were hit by strikes last week.

The Belfast Office of Industrial Tribunals and Fair Employment Tribunal was also closed.

Nipsa General Secretary John Corey said there would be no let-up in the industrial action until negotiations achieved an acceptable resolution.

"Members have been supporting this industrial action campaign for over three months and hundreds of members have been involved in rolling selective strike action for over seven weeks," he said.

"There has been ample time to negotiate a fair resolution of this dispute.

"Nipsa is ready to negotiate, but discussions so far have not made any progress towards a settlement."

The department has said it was intent on protecting "our obligation to customers and minimise the impact of the strike".

Thousands of civil servants have taken part in a series of strikes since late last year over being denied a "cost of living" pay increase from April 2003.