PEOPLE who are terminally ill in palliative care units and some cancer patients will be among the thousands affected when junior doctors walk off hospital wards.
The junior doctors, who are protesting against long working hours, will only provide Sunday levels of cover in the palliative care units which are not exempted from the action.
Cancer patients whose treatment is not assessed as urgent are also having their appointments postponed as a result of the action, although all others are going ahead.
Thousands of other waiting-list patients will not undergo surgery or see a specialist today as a result of the walkout.
Around 3,000 junior doctors will picket hospitals across the country today for the first time in a quarter of a century.
A spokesman for the Irish Medical Organisation (IMO) said the doctors regretted the inconvenience to patients but insisted "the responsibility lies with the Health Service Executive (HSE)".
The hospitals will be reduced to Sunday levels of cover by the junior doctors, causing disruption to thousands of patients who may have waited months or even years to be treated.
The action, starting at 7am, will also cause delays for people turning up at hospital emergency departments if their conditions are non-life or limb-threatening.
"Weekdays, particularly Monday, Tuesday, and Friday are considerably busier and therefore Sunday levels of staffing are unlikely to be adequate to manage patient demand, inevitably resulting in delays," warned emergency doctors' spokesman, Dr Cyrus Mobed.
Hospitals said they had reviewed appointments by theatre and clinic. Patients are advised that unless they have been contacted by phone and told their procedure has been cancelled they should turn up as normal.
Hospital consultants, nurses and other health staff will be on duty and are not involved in the action. However, Nurses say they will not take on the work normally done by junior doctors.
Urgent cancer and dialysis care will go ahead. An experienced junior doctor will be on standby for intensive care units and they will respond to any major incident such as a serious crash involving severe injuries.
It is unclear if around 1,900 junior doctors who are not members of the IMO will turn up for work.
The junior doctors want an end to shifts of more than 24 hours and the introduction of a 48-hour week by the end of next year, as well as workable sanctions for hospitals that fail to operate the new rosters.
Dr John Donnellan, spokesman for junior doctors in the IMO, said: "Our members are worried for the risks which the dangerously long hours they have to work pose to their patients and to themselves."
The IMO rejected calls to return to the Labour Relations Commission because they claimed the HSE sanctions for hospitals breaching the working limits were not enough.
HSE chief Tony O'Brien said he hoped that patients who suffered cancellations would get a new appointment as quickly as possible.
"Our ability to do that is dependent on a quick resolution to this dispute and no further withdrawal of labour," he warned. "It is not tenable for patients to be subjected to rolling action, regionally or nationally."