The Irish Nurses and Midwives Organisation (INMO) say any improvement to hospital overcrowding in 2018 is unlikely unless "drastic and innovative steps" are taken.
It comes as the INMO annual trolley and ward watch figures recorded over 300 patients waiting on trolleys or on additional beds in the final weekend of the year.
Overall throughout 2017, 98,981 admitted patients were recorded as awaiting on a hospital bed.
University Hospital Limerick recorded the highest annual number of 8869; Cork University Hospital and University Hospital Galway saw 6815 and 6563 respectively.
And the Mater University Hospital in Dublin was the capital's most overcrowded hospital, with 5238 patients on trolleys during 2017.
Smaller hospitals, such as Our Lady’s Hospital in Navan, showed increases from 595 in 2016 to 2435 in 2017 - and Portiuncula Hospital in Ballinasloe recorded 1569 trolley figures compared with 892 in 2016.
Phil Ni Sheaghdha is general-secretary of the INMO.
"Overcrowding in late December and early January is getting worse. Despite investment in winter plans, smaller hospitals are now severely overcrowded which is manifestly unsafe and leads to higher cross infection and poorer outcomes for patients.
"Nursing staff, constantly working in this high pressure, unsafe environment, cannot be expected to put up with this obvious neglect of duty of care to them and the patients they try to care for any longer.
"It appears to me, that staff and patients, on the front line, were abandoned while the system shutdown for Christmas and the New Year."
Ms Ni Sheaghdha said there is a system of de-escalation which is mandatory for hospitals to follow, before spreading overcrowding to the entire hospital, which was abandoned during the Christmas period.