Contract cleaners and catering staff at Tallaght Institute of Technology are to begin industrial action next week.
The move follows the refusal of a new contractor to retain the 16 staff members under a transfer of undertakings arrangement.
Siptu said the dispute arose after the original contractor, Resource, told staff they were being let go because the new company, One Complete Solution (OCS) was not going to take them on.
A statement from the union said that the action will begin on the last day of the cleaners' current contracts and they would continue their pickets for as long as it takes to secure their jobs.
According to Siptu branch organizer Bernie Thornton the custom and practice amongst cleaning contractors is that a transfer of undertakings should apply in this situation, however Resource will be issuing its 16 workers with P45s with effect on June 30th. She said this behaviour would "not be tolerated by our members and OCS is morally wrong to treat people in such a deplorable manner".