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.”
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.”