The INMO say they fear "the situation may deteriorate" in the coming days
The Health Minister Simon Harris is considering extending hours for some hospital services, to deal with the latest spike in hospital overcrowding.
He was responding to new figures, which showed a record number of 612 people on trolleys in emergency wards Tuesday morning.
Minister Harris says the surge is the result of a strain of influenza, which is affecting older people particularly harshly.
He says the best way to stop the problem escalating is to get vaccinated.
He has also outlined some of the options available to help reduce the numbers on trolleys.
"One is the idea of extending access to diagnostics in our hospitals until 8pm several nights a week from now until the Spring.
"A second is reviewing the length of stay for all of the patients who may be were admitted during the Christmas period, and are now fit to go home.
"A third is working with our nursing homes - particularly in relation to our frail elderly".
Trolley and ward watch figures from the Irish Nurses and Midwives Organisation (INMO) show University Hospital Limerick is the most overcrowded, with 46 people in need of a bed.
The Midland Regional Hospitals in Portlaoise and Tullamore, St Luke's Hospital in Kilkenny, and University Hospital Galway all have 40 or more patients on trolleys.
The INMO also says there were a record 93,621 admitted patients on trolleys over the course of 2016 - a record figure for a calendar year.
INMO General Secretary Liam Doran said: "612 patients, admitted for care, for whom there is no bed, is a truly shocking figure. The compromising of care, not to mention the loss of privacy and dignity, cannot go unchallenged and must be acknowledged and addressed by health management.
"We cannot allow this to become just another statistic and it must result in a fundamentally new approach to our health system as overcrowding, as the 2016 figures confirm, continues to grow."
He added that his organisation fears the situation may deteriorate further in the coming days, due to the current flu situation and closed beds due to staff shortages.
"An emergency response is now required and this must be forthcoming, from health management, immediately," Mr Doran said.
He added that "it is proof, if it were needed, that the health service is still too small to cater for demand".
Fianna Fáil's spokesperson on health, Billy Kelleher, suggested that "hospitals in Cork, Limerick, the Midlands and Donegal are creaking with the pressure being put on them".
In a statement responding to today's figures, he said: "It has now gotten to a stage where the HSE believes that 300-400 patients every day are lying on a trolley waiting for admission is acceptable. It’s not, and the Minister needs to bring forward proposals that increase capacity in our hospital wards and ensure those that need a ward bed get one as quickly as possible.
"Right across the country, there are community hospitals with fully functioning wards that could be used to treat non-acute patients, thereby freeing up acute beds in our major hospitals. It’s time for the Minister for think outside the box to find a permanent solution to hospital overcrowding."
Sinn Féin's Louise O'Reilly, meanwhile, argued: "It is clear that the government has no plan to deal with this escalating crisis and no strategy that will reassure overworked staff that this will not be another year of unacceptable overcrowding.
"This is utterly unacceptable and a bad start to the New Year for patients and health workers," she added.