There are 620 patients on trolleys in hospitals around the country, with a record high of 73 waiting in Cork University Hospital (CUH).
The majority of those waiting for beds in CUH are elderly patients.
"This is a crisis situation. Our members on the frontline are describing the situation as 'horrendous' for both staff and patients," said Liam Conway, who is the INMO's Industrial Relations Officer for CUH.
Mr Conway is urging the HSE to intervene with measures such as cancelling elective surgeries in CUH until the bed situation is resolved.
"We are calling for the hospital to fully implement de-escalation policies. This means cancelling electives, stopping non-emergency admissions, and sourcing extra bed capacity from the private and public sector services. This de-escalation should continue next week, until the hospital is stabilised.
"There have been over 50 nursing vacancies in CUH for several months, due to the HSE's cost-cutting 'go-slow' recruitment policy. After much lobbying, we got the HSE to approve recruitment for the posts on December 20 - far too late to make a difference this winter."
According to the INMO, 433 patients nationwide are waiting in the emergency department, while 187 are in wards elsewhere in the hospital.
Last year, over 118,000 patients found themselves waiting for a bed in hospital.
Today's figures come as the South/ South West Group urges the public to prevent the spread of flu by avoiding hospitals, congested emergency departments and contacting GP surgeries by phone, so as not to infect others who may be very unwell already.
"Mild illnesses such as colds, sore throats, coughs and such like, are usually viral, self-limiting illnesses and can be treated at home with fluids, over-the-counter painkillers and rest," said Dr. Paul Gallagher, consultant geriatrician at CUH.
"Antibiotics will not work on a viral infection, including flu. Get plenty of rest, drink lots of fluids and take paracetamol or ibuprofen for temperatures, aches and pains. You can visit www.hse.ie/winter or www.undertheweather.ie for useful advice and self-care tips for treating mild viral illnesses”.
Management of the South/South West Hospital Group have requested that members of the public contact their GP or South Doc before attending the Emergency Department if their needs are not urgent.