Fears have been raised that contingency plans for a strike-hit Ambulance Service could threaten patient safety in Northern Ireland.
housands of union members - including those representing nurses, paramedics, hospital porters and ambulance crews - will walkout from midnight tomorrow.
Concerns have been voiced that the Ambulance Service could be under pressure to cope with 999 calls, especially in rural areas.
But unions have insisted that patients will receive safe care.
On Thursday morning the Unions confirmed that 'emergency cover' for the Fire and Ambulance Service would be provided on the day of action.
The Northern Ireland Ambulance Service has said there will be voluntary ambulances used to provide cover with 10 St John ambulances made available.
Unite National Officer Kevin McAdam said: “Industrial action is a last resort for Unite but our members have no alternative. They rightly fear that the scale of the proposed cuts to public services – including to NI Ambulance Service and NI Fire & Rescue Service – will undermine these critical services and threaten public safety.
“In order to ensure that members of the public are not put at risk on Friday, Unite and the other unions representing staff within the Northern Ireland Ambulance Service have agreed an overarching protocol which provides emergency cover during industrial action. Our members will observe this protocol as our focus is on maintaining public safety.
"The protocol allows local initiative in response to emergencies. Unite has put in place similar arrangements in the NI Fire & Rescue Service where our members will ensure that no vehicles are left ‘at risk’ during the strike action."
Department of Health officials say arrangements have been put in place to ensure that critical services will be maintained.
But it confirmed that as part of the contingency plans, non-critical planned procedures and appointments will be cancelled.
GPs have said that the pressures on ambulance services are bound to be affected by the walk-out.
Emergency cover will be provided for hospital wards and emergency theatres. It is understood Northern Ireland Ambulance Service managers will also provide cover, taking 999 calls.
The Royal College of Nurses and Royal College of Midwives voted not to go on strike.
However, Eoin Stewart, co-chair of the Unison NI Forum, said nurses will also be involved in the industrial action.
"There is approximately 12,000 registered nurses with Unison, that is not including healthcare assistants," he said.
"Nurses don't take this action lightly but we have a responsibility to our patients and professional standards are required to be adhered to, but are now under severe pressure due to budget cuts."
Dr John O'Kelly, a GP and chairman of the Royal College of General Practitioners NI, said: "The major concerns are over emergency ambulances and there is still uncertainty over what will happen."
Former Health Minister Michael McGimpsey said he shared concerns about patient impact.
A spokesperson from the Department of Health said: "For the duration of the industrial action cover will be provided for emergency services and activities, procedures and appointments."
A spokeswoman for the Health Board said: "Where outpatient appointments are cancelled by trusts, every effort will be made to reschedule these into the next available slot, and this should be within six weeks. Trusts will be informing patients directly if their appointment is to be rescheduled."