Up to 20,000 civil servants across the North are staging a one-day strike as part of a continuing pay dispute.
It is the third day-long stoppage by members of the public service union Nipsa and follows three days of disruption to government offices this week when telephonists went on strike.
Next week, more than 20 veterinary and meat inspection staff at the Department of Agriculture in Belfast are to mount an extended strike which the union expects will force the closure of two key meat plants in Ballymena and Crumlin, Co Antrim.
The union say the dispute is over the failure of the Government to provide civil servants with a cost-of-living pay increase from April last year.
General secretary John Cory claims finance minister Ian Pearson's assertions that staff were receiving a 3.67 per cent pay increase were fictional.
PA