Almost 2,500 staff at social security offices across Northern Ireland are to strike later today over plans to extend opening hours.
Union leaders said 2,300 staff at 35 public offices, where pensions and unemployment benefits are collected, will hold a half-day stoppage from lunchtime.
Mr Tony McMullan of the Northern Ireland Public Service Alliance (NIPSA) union accused management at the Social Security Agency of being inflexible after they proposed offices stay open for an extra hour until 4.30 p.m.
"Management were refusing to provide any additional resources in order to cope with this extra workload," he said.
"And obviously our members are not prepared to take on additional work and as well as that to forego the opportunity to be able to work the flexible working hours scheme."
However, the Social Security Agency said there would be no changes to the terms and conditions of staff.
It said the union had called the strike among its members "because they were being required to keep offices open to 4.30 p.m."
"Staff are being asked to extend the time they spend with the public, not to work any extra hours," a spokesman said.
"They are not having their terms and conditions changed. Staff have always been required to work normal office hours."
The spokesman said it was disappointing that NIPSA had decided to advise their members to take this "inappropriate action".
"Social security customers are entitled to a service at least comparable to the services received from other public sector organisations," he said.
"Most other public sector organisations open their public offices to at least 4.30pm. Social security customers should expect this at the very least.
"The issue of extending public office hours to 4.30pm is not new to NIPSA representatives, it has been the subject of consultation for the past 15 months.
"In that time NIPSA has not raised one legitimate objection to the Social Security Agency improving customer services this way.
"However, even at this stage we are willing to talk to NIPSA if they agree to call off their industrial action," he added.
PA