The Health Minister says he can't understand why the union representing health support staff went ahead with a strike before going to the Labour Court.
10 thousand workers including cleaners, porters and catering staff have downed tools today in a pay dispute.
The HSE says we won't know the full impact on hospitals until later today, but that surgeries, inpatient procedures and outpatient appointments will be the areas worst affected.
The SIPTU union doesn't think going to the Labour Court now would resolve the row, if the goal posts in the dispute continue to change.
But Health Minister Simon Harris insists that's what needs to happen to avoid more strikes next week: