The INMO wants the HSE to develop a hospital-by-hospital plan to ensure the system is not "completely overwhelmed" by the end of the Easter Bank Holiday.
It says "we're coming out the other side of another bank holiday where hospital overcrowding remains completely out of control."
Figures from the Irish Nurses and Midwives Organisation today show 651 people, including 14 children, are waiting for a bed in hospitals nationwide.
University Hospital Limerick is the worst affected by overcrowding today, with 119 patients on trolleys - while there were 23 patients admitted to University Hospital Kerry without a bed to accommodate them.