Picket lines took place outside Craigavon Area Hospital, Lurgan Hospital, Portadown Health Centre and Banbridge Health Centre.
The workers are striking over a proposed 4% pay offer which they say is well below the level of inflation.
NIPSA Deputy General Secretary, Pádraig Mulholland, said: “"We must have inflation busting pay rises for all health service workers and an end to the chronic understaffing that puts lives at risk.”
1. 'If our pay doesn't rise we will'
Members of Unison at the picket line at Craigavon Area Hospital on Monday. Health workers were taking part in a 24 hour strike over pay. Photo: Carmel Robinson
2. On the picket line
Health workers on the picket line outside Lurgan Hospital on Monday. Workers were on a 24 hour strike over pay. Photo: Contributed
3. 'Safe staffing saves lives' says the slogan at the picket line
Members of Unison take part in a picket at Craigavon Area Hospital on Monday. Health workers were on a 24 hour strike over pay. Photo: Carmel Robinson
4. Wrapped up on the picket line at Craigavon
Ambulance staff as well as other health care workers across the Southern Health Trust joined union colleagues from across Northern Ireland to stage a 24 hour strike over pay on Monday. Photo: Carmel Robinson