Around 150 workers at Birmingham and Solihull Mental Health NHS Foundation Trust were set to strike for three days next week.
The porters, housekeepers, domestic assistants and maintenance staff, members of the Unison and Unite unions, will be out from Monday to Wednesday.
They are fighting plans to move them from direct NHS employment to working for Summerhill Services Limited on 1 July.
Unite regional officer Frank Keogh said, “This will strip members of their status as NHS employees and is a part of the backdoor privatisation of the health service.”
The Unison union last week won an important legal judgment affecting NHS workers.
It means those staff who do overtime on a regular basis or frequently work beyond their normal shifts should have these extra hours taken into account when their holiday pay is calculated.
Previously, NHS workers who regularly did extra hours saw their pay fall when they took a holiday.
The ruling could benefit tens of thousands of NHS staff who are employed under the Agenda for Change payment system.
News in brief from workers' struggles
Outsourced cleaners are fighting back
Organise to finish fascist Tommy Robinson