Nurses and midwives have begun their first 24 hour strike.
INMO members from the 4 hospitals in the South East are among the 37,000 people demanding pay restoration and government action on staff shortages.
The HSE says it won't be a "normal day" for the service with 25,000 appointments cancelled.
People are also being advised to only attend emergency departments if it's essential.
These INMO members are on the picket line outside University Hospital Waterford.
Mary Dunne is a nurse, and is also running the strike committee at University Hospital Waterford, she says it was a necessary step to strike:
Emer is one of the nurses on the picket line at Wexford General Hospital, she remembers Taoiseach Leo Varadkar when he worked in the hospital as a doctor:
Dr. Colm Henry, Chief Clinical Officer with the HSE, says delays in accessing services today are inevitable.
"People may experience increased delays because other aspects of unscheduled care such as local injury units or acute medical assessment units will not be open," said Dr Henry.
Further strikes are planned for next week.
As the Labour Court says it cannot intervene in the dispute, it is up to the INMO and the HSE to resolve it.
