A number of other healthcare staff are also to take industrial action over pay and conditions.
Unite’s Ambulance Service members will join Translink workers for a 24-hour stoppage on May 6.
Meanwhile, Unison expects thousands of its members across all health service settings to respond to the call to withdraw additional, voluntary, unpaid and goodwill time for two weeks.
The action began this Monday and will continue until Sunday, May 10.
A Unison spokesperson said, “Our members are already putting their shoulders to the wheel in holding up a creaking and dysfunctional and over bureaucratised health service.
“They have taken to the streets for months now in solidarity with and giving strong support to communities resisting cuts to services.
“Now they have to deal with the added insult of a pay deal for last year which was the worst across the four NHS jurisdictions and no offer at all for 2015/2016. Their actions should illustrate the huge amount of goodwill and the big contribution they make.”