Hospital emergency departments face industrial action this month after nurses belonging to the Irish Nurses and Midwives Organisation rejected settlement proposals aimed at addressing overcrowding and staff shortages.
The proposals, negotiated with the HSE at the Workplace Relations Commission last month, were rejected by a margin of 58% to 42%.
INMO General Secretary Liam Doran said the union will now proceed with further industrial action on 14 and 26 January.
He said the main reason the deal was rejected came down to a complete lack of confidence among ED nurses that management at hospital and group level would actually implement the proposals.
He said the situation was exacerbated by the increase in trolley numbers in recent days.
Minister for Health Leo Varadkar said he was disappointed by the rejection of the proposals.
He said strike action during the busiest time of the year will not resolve overcrowding but will compromise patient safety.
He called on nurses not to go ahead with the strike to "allow time to pause for reflection".
Earlier today, the INMO said there are 558 patients on trolleys in emergency departments or on wards waiting for admission to a hospital bed.
The figure represented an increase of 42 on yesterday.
The worst affected hospital is Beaumont in Dublin, where 49 patients are waiting.
The public have been asked to avoid or delay visits to the emergency department at the hospital.
Other hospitals badly affected include St Vincent's, also in Dublin, with 43 patients waiting and Cork University Hospital where 42 are waiting.
In a statement the Health Service Executive said it remains hopeful that further talks "regarding the implementation of the Escalation Policy at local level, may assist in resolving matters and prevent industrial action".