The INMO has called for all non-urgent elective procedures to be cancelled as it said there were 640 admitted patients, including 27 children, waiting for a bed at hospitals around the country.
It said the overcrowding is leading to "very dangerous situations for patients and nurses".
Irish Nurses and Midwives Organisation General Secretary Phil Ni Sheaghdha said hospitals "must make it their focus to de-escalate the number of patients being admitted on trolleys".
The hospital worst affected this morning is University Hospital Limerick with 109 patients waiting for a bed.
Yesterday, there were 132 patients waiting for a bed at UHL, according to the INMO's figures.
There were 94 patients waiting at Cork University Hospital; 73 at University Hospital Galway, and 54 at Tallaght University Hospital in Dublin.
The INMO said there were 16 children waiting for a bed at Children's Health Ireland Crumlin, with seven at the National's Children's Hospital, Tallaght, and three at CHI Temple Street.
