Junior doctors have warned that tomorrow's one day strike at 51 hospitals may not be the last.
More than 3,000 medics have prepared to force hospitals into a Sunday standard service from 7am to midnight in an unprecedented action over working hours.
Negotiations with the Health Service Executive (HSE) repeatedly failed to find a resolution to the row over non-consultant hospital doctors working shifts in excess of 24 hours.
Eric Young, assistant director of industrial relations at the Irish Medical Organisation (IMO), said the HSE ignored the issue for too long.
"It has relied on the goodwill and professionalism of our members to continue working illegal working hours," he said.
"They can no longer take our members for granted. They must demonstrate a commitment to engaging with our members in a serious and credible way or there will be further disruptions ahead."
Doctors have committed to provide Sunday standard cover in the hospitals with one additional on-call registrar for intensive care units. They will also carry out any required transplant and dialysis service and the normal weekend palliative care.
They will also attend for patients who are undergoing active chemotherapy and radiotherapy which cannot be deferred and a ny unforeseen major incident.
Even at the 11th hour the HSE were still trying to get the IMO back around the talks table in the Labour Relations Commission.
Tony O'Brien, HSE director general, said thousands of inpatients and outpatients were being disrupted.
"It's very regrettable," he said.
"It is critical even though at this point, it now seems inevitable, avoidable but inevitable, that there will be a withdrawal of labour tomorrow.
"Our aim will be to get the talks back on as quickly as possible. I see no necessity, desirability or point and any further industrial action beyond tomorrow."
The IMO claim that junior doctors are routinely asked to work 24 hour shifts and on some occasions up to 36 hours and up to 100 or more hours a week.
Dr John Donnellan, of the IMO's non-consultant hospital doctors' committee, said many complain of exhaustion and stress and risk to patient safety.
"Our members are worried for the risks they pose to their patients and to themselves by current working conditions," he said.
"Current working arrangements are in breach of European directives and even the Minister for Health has criticised them. The challenge now is to bring them to an end as quickly as possible."
Sinn Fein health spokesman Caoimhghin O Caolain appealed for Health Minister Dr James Reilly to intervene at the 11th hour.
"James Reilly, as current minister for health and former president of the Irish Medical Organisation, is uniquely positioned in the current dispute between junior doctors and the HSE regarding working hours and conditions," he said.
"I am making an appeal to him to use that position to make an 11th-hour intervention, personally, in an effort to overcome the difficulties that still remain within the negotiations and to avert the now signalled strike action by junior doctors scheduled to commence tomorrow."
Meanwhile, the Irish Association for Emergency Medicine (IAEM) warned that the staffing levels will not be strong enough to cover patient levels in the emergency wards of the hospitals.
"It is important for the public to realise that while emergencies will continue to be managed during any industrial action, there will be disruption to services and delays for patients. These delays are most likely to affect those with non life or limb threatening conditions," a spokesman said.