Strike action by civil servants has spread to the planning office in Belfast, and is due to be joined by staff in Omagh, Co Tyrone, today.
The industrial action marks a worsening of a nine-month dispute over pay called by the Northern Ireland Public Service Alliance (NIPSA).
Planning applications and decisions in the greater Belfast area are to be affected, and knock-on effects are now anticipated west of the Bann.
The union, which represents public sector employees, claims its members have not received any cost-of-living pay increases since April 2003. Last week it refused a revised government pay offer of just over 4.6 per cent over 16 months and talk of "flexibility to address the problems".
The action has already resulted in the cancellation of thousands of driving tests and compulsory vehicle tests.
Centres run by the Driver, Vehicle and Testing Agency (DVTA) at Belfast, Mallusk and Lisburn, Co Antrim; Armagh city, Craigavon, Co Armagh; and Newtownards and Newry, Co Down, are affected.
The government had initially offered a pay package which would add 3.67 per cent to the wage bill of the Northern Ireland Civil Service. However, the union said that was part of a pre-agreed increment, and took no account of the rise in the cost of living.
All-day talks involving the union and the government broke up without agreement last month.
Mr John Corey, NIPSA's general secretary, said yesterday the action would continue by Department of Agriculture staff, which would affect farmers' grants.