The Irish Nurses and Midwives Organisation (INMO) said a return to major overcrowding in University Hospital Limerick (UHL) must be stopped.
42 patients are on trollies in UHL which according to the union is more than half of all patients on trollies in Ireland.
22 people are on trollies in the emergency department and 20 people are on trollies elsewhere.
The INMO said there were 74 people on trollies nationally.
The union is calling for national intervention to prevent further negative outcomes for patients and frontline healthcare workers.
In a statement, the INMO said they are calling for "direct national oversight and investigation as to what is causing this overcrowding."
Mary Fogarty, INMO assistant director of industrial relations for the region, said trolley numbers are low as many health services are reduced at this moment and capacity has been increased.
“Yet what we are seeing in Limerick is beyond belief. UHL has more patients on trolleys today than all other hospitals in Ireland put together," she said.
Ms Fogarty said overcrowding is unacceptable at the best of times but presents a serious risk during the Covid-19 crisis.