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.”
5. All wrapped up for the picket line
Brrrrr - a very cold day did not deter health workers from attending the picket line outside Banbridge Health Village, Co Down. Photo: Contributed
6. Dancing on the island to keep warm while on strike
Health care workers from across the Southern Health Trust were demonstrating at the picket line close to Craigavon Hospital on Monday against the latest pay offer. Some union members were dancing to keep warm as vehicles driving past tooted in support. Photo: Carmel Robinson
7. Braving the frost on the picket line
Health care workers from Craigavon Hospital and from across the Southern Health Trust took part in a 24 hour strike on Monday in a quest for a better pay deal. Photo: Carmel Robinson
8. All wrapped up for the picket line
At Craigavon Hospital health care workers were vocal in their call for fair pay as they staged a 24 hour strike on Monday. Photo: Paul Cranston