10,000 health workers will go on strike on Wednesday if further talks on Monday aren't successful.
Support-staff at various grades are involved in a row over pay and a jobs evaluation scheme with the HSE.
Talks took place between both sides at the Workplace Relations Commission over the last two days.
After some progress, it was announced that Tuesday's strike was called off.
But SITPU's Paul Bell says as things stand, a 24-hour stoppage will go ahead at 38 hospitals and health facilities on Wednesday.
He says the union deferred last week's strike at the request of the WRC but if there is not a successful outcome on Monday, the union is adamant that Wednesday's strike will take place.