Health services are to be severely disrupted on Thursday - with 10,000 staff to strike.
Staff at various support-staff grades, including chefs, porters and healthcare assistants, are involved in a pay dispute with the HSE.
Talks aimed at resolving the row ended without agreement at the Workplace Relations Commission last night.
Discussions will take place today between the HSE and SIPTU on back-up plans for Thursday's strike.
Siptu's Paul Bell said the strike is now a certainty.
He said: "We will have strike action...there will be some discussion about a limited amount of contingency, but that will have to be agreed locally as identified as required.
"That's the position that we are in now. We will try our best to work with our colleagues on each location and indeed to ensure patients have a limited impact on themselves."