The INMO has called for a meeting with the Emergency Department Task Force as a "matter of urgency", as 457 patients are waiting admission to a hospital bed, including 101 patients at University Hospital Limerick.
The Irish Nurses and Midwives Organisation said it has requested a meeting with the Task Force three times, but said the response from the Health Service Executive has been "inadequate".
INMO General Secretary Phil Ní Sheaghdha said: "The numbers of patients without a bed in Irish hospitals is completely unacceptable.
"For there to be 457 patients without a bed on a single day in the middle of June is not something we should accept as a given."
She called on the Health and Safety Authority to act on the "unsafe" conditions nurses are working in and said the "dignity of patients is often diminished because of the conditions they are being treated in".
Ms Ní Sheaghdha said nurses cannot provide the clinical care that is required and are "burnt out both physically and mentally".
She said: "Our nurses are at the end of our tether" and the "slow reaction and at times hands-off approach from their employer will drive many nurses out of the profession".
She said the union believes its Emergency Department agreement brokered with the HSE is being ignored and has referred it back to the Workplace Relations Commission.
"At this juncture without real focus and input we will have no other option but to discuss industrial action with our members in emergency departments," she said.
Other hospitals affected by overcrowding this morning are Sligo University Hospital with 51 admitted patients waiting for a bed; 38 at Cork University Hospital and 33 at the Mater Hospital in Dublin.
