10,000 HSE support staff at 38 hospitals are set to take part in 24 hours of industrial action, after there were no moves to break the deadlock between SIPTU and health service management side over pay.
While some contingency cover is being agreed at local level in the 38 affected hospitals, the strike is expected to disrupt scheduled inpatient procedures, scopes and theatre activity, as well as outpatient appointments and even catering.
Patients facing cancellations are being notified by individual hospitals, but the HSE has previously acknowledged that the dispute will ultimately contribute to longer waiting lists, as did the strike by nurses and midwives earlier this year.
The dispute centres on a job evaluation scheme, which the Government agreed to carry out during negotiations on the last Public Service Stability Agreement (PSSA).
The job evaluations examine whether roles have changed and whether pay rises are warranted.
Affected grades include health care assistants, maternity care assistants, laboratory aides, chefs, and surgical instrument technicians, as well as workers in portering, household and catering services.
Apart from tomorrow's 24-hour stoppage, SIPTU has scheduled three further back-to-back strikes on Tuesday, Wednesday and Thursday of next week.
The union has also threatened to escalate the dispute by balloting staff in at least 20 other hospitals for strike action, if its grievances are not addressed.
Sligo-based Emergency Medicine Consultant Fergal Hickey confirmed that emergency services will be significantly impaired if tomorrow's stoppage goes ahead, particularly because of the wide range of activities affected.
He said he was not concerned that patients would be put at risk of imminent death, but warned the strike would have significant implications for patients and the running of the health service.
Mr Hickey also voiced concern that SIPTU and management would now become more entrenched, making it even harder to reach agreement.
HSE National Director of Community Operations David Walsh has said it is working to ensure that an essential level of service is provided to patients in hospitals.
Speaking on RTÉ's News at One, he said that across the 38 affected sites, management was engaging with SIPTU representatives on contingency arrangements to try to minimise the disruption.
But he said there would be disruption and services would be cancelled with outpatient, day case and elective inpatient procedures affected.
Mr Walsh said the HSE was looking for derogations from SIPTU for essential services, such as catering.
He said those whose procedures have been cancelled will be contacted by the HSE and the procedures will be rescheduled as quickly as possible.
Mr Walsh added that if the three strike days planned for next week go ahead it would have "a very significant effect on the HSE's ability to provide service".
Minister for Health Simon Harris said it was extraordinary that SIPTU would go on strike without going to the Labour Court first.
He also noted that the Government side had conceded significant ground in moving from its original position of no payments of increases before 2021, to beginning payment in October of this year.
He described this as a significant offer, particularly in light of Brexit.
However, SIPTU Health Division Organiser Paul Bell said that procedures at the Workplace Relations Commission had not been exhausted, as some issues had not even been discussed and so it would be premature to refer the matter to the Labour Court.
He also claimed the Government was only offering a fraction of the monies due to his members.
Mr Bell accused the management side of trying to change to terms of the job evaluation scheme at the centre of the dispute in a way that would reduce the gains for staff.
Taoiseach Leo Varadkar said the offer to go the Labour Court still stood and that he regretted the union was not prepared to do this.
Speaking during Leaders' Questions in the Dáil, Mr Varadkar said the Government accepted the outcome of the job evaluation process that would see phased increases for health workers, but the dispute remained around the timing of its implementation.
Fianna Fáil leader Micheál Martin said it was striking the Taoiseach was acknowledging the increases had not been provided for in the budgetary figures, but saying the Government accepted they had to be paid.
Mr Martin said the reason why SIPTU was reluctant to go to the Labour Court was because the Government had been dragging its feet and was not was serious about the implementation of the job evaluation process recommendations.
Sinn Féin's Pearse Doherty said the strike would go ahead unless the Government lived up to promises made four years ago.
He said the workers involved do invaluable work and deserve to be paid accordingly.