The Irish Medical Organisation has said tomorrow's one-day strike by junior hospital doctors is "a necessary evil" brought on by inaction by the Health Service Executive over long working hours.
IMO's junior doctor group chairman Dr John Donnellan said the union will review matters after the strike to see what further industrial action might be needed to force change.
The planned strike action has already caused the deferral of 12,000 out-patient appointments and 3,000 planned operations.
HSE Director General Tony O'Brien said the strike seems inevitable but is still avoidable.
He said the HSE would reschedule appointments, but this would depend on no further strike action and an early resolution.
Mr O'Brien also said it was disappointing that strike action would take place in hospitals that were already compliant on hours.
Emergency services, oncology and other key services will be protected during tomorrow's action.
Public hospitals will operate a service that would normally be provided on a Sunday.
IMO refuses LRC return
Agreement has not been reached between the two sides despite lengthy talks at the Labour Relations Commission and a set of proposals from HSE management.
The IMO has refused an invitation to return to the LRC, as it believes the HSE proposals lack credibility.
Minister for Health James Reilly has claimed there is little between the sides and has appealed to doctors to go back to the LRC and not to take action that would affect patients.
The IMO is also considering a two-day strike next week, which will affect 36,000 appointments.