The INMO is consulting its members this week about possible strike action.
It says hospital staff currently don't feel safe, while they can't guarantee patient safety because of the overcrowding situation.
The union's comments come as Cork University Hospital is the most overcrowded hospital in the country today with 56 people on trolleys
Nationally there are 534 patients on trolleys in Irish hospitals today - an increase of 45 from yesterday.
INMO general secretary, Phil Ni Sheaghdha says their members have been let down:
"I believe fundamentally that there's been an omission of care for those that work in the health service, particularly nurses and midwives, because the assaults and the figures that are recorded by the employer of assaults against nurses is on the increase. And it's unacceptable. In our view, the employer is not upholding its responsibility to keep their workers- in this case nurses and midwives- safe."
