Talks at the Labour Court aimed at resolving a pay dispute at the National Ambulance Service are due to resume today.
SIPTU and Unite met with HSE management on Monday and Tuesday, but SIPTU has described the discussions as "difficult" and said agreement has not yet been reached.
"The Labour Court has asked the parties to return this Thursday as a final opportunity to try to resolve the dispute before next week's industrial action," the union said in an update to members.
SIPTU's Ambulance Sector Organiser John McCamley thanked the union representatives for taking part in the talks.
"I share their disappointment that more progress has not been made, but union representatives want to make sure they get the best possible deal on offer," Mr McCamley said.
A 24-hour strike by frontline ambulance workers took place last week, with the HSE saying it had a "significant impact" on services.
A planned 48-hour strike, which was due to be held this week, was stood down to allow for talks at the Labour Court.
Plans remain in place for a 72-hour work stoppage on 26 May.
A work-to-rule by frontline ambulance staff, which began last week, is also continuing.
Unions have accused the HSE of failing to implement the recommendations of an independent report on updating staff salary scales to reflect changes in responsibilities and workload.
The HSE said that previous proposals to resolve the dispute, that would have delivered pay increases, were rejected.
Unions said however that the proposals came with conditions, including changes to allowances, that were unacceptable to members.
