A record number of patients are waiting admission to a hospital bed at University Hospital Limerick, according to the INMO.
The Irish Nurses and Midwives Organisation said 97 patients - 54 in the emergency department and a further 43 elsewhere in the hospital - are listed on the daily INMO Trolley Watch list.
This is the highest since 16 November, when 95 patients were recorded as waiting admission to a hospital bed.
The hospital is frequently listed as the most overcrowded hospital in the country, with daily high numbers waiting in its emergency department and on wards.
Cork University Hospital is the next busiest with 57 patients waiting, and there are 48 patients waiting admission to a hospital bed at University Hospital Galway.
The INMO has called on the Health Information and Quality Authority to investigate the overcrowding issue at UHL.
Mary Fogarty, INMO Assistant Director of Industrial Relations, said: "Today's trolley numbers in University Hospital Limerick are extremely concerning. Time and time again, University Hospital Limerick is the most overcrowded hospital in Ireland.
"Despite major investment in capacity at the hospital, it is making no dent in the consistent overcrowding problem in the hospital. Overcrowding adds stress for staff and worsens patient care. It is high-risk in normal times, but even more so during a pandemic.
"The INMO is once again calling on HIQA to urgently investigate the overcrowding issue in the hospital and make recommendations.
"The patients and nurses at University Hospital Limerick deserve better than these conditions. It has been an extremely difficult 22 months since Covid first arrived on our shores but UHL was already overstretched without being dealt with the hand of a pandemic.
"The staff, patients and wider community in Limerick need to be assured that the long-standing issues at UHL will be resolved."
Meanwhile, the Health Service Executive has said that the current guidance on visiting for acute hospitals and nursing homes remains in place.
It said that healthcare settings are quite different from other contexts in which people gather together for work, or social interaction.
The HSE said that people with infectious Covid-19 in need of healthcare may need to attend healthcare settings introducing a risk of infection.
It added that many of those most vulnerable to the consequences of Covid-19 infection are also present in healthcare settings.
For this reason, "a greater degree of caution is required in healthcare settings" compared to other settings.
Across the health system, visiting is temporarily suspended in many cases, however exceptions are made in certain circumstances, including for maternity services, on compassionate grounds, or where a patient is in ICU.
Details of the various visiting restrictions for each hospital are on the HSE website.
The HSE said that guidance is regularly reviewed and updated and recent NPHET decisions are taken into account in guidance reviews.
The Irish Patients Association has said that overcrowding in emergency departments extends the pain and suffering caused by patients having their operations cancelled.
It said the cancellation of operations as a response to overcrowding should be an exception, and not part of the day-to-day management of patient flow.
Additional reporting Fergal Bowers