There were 1,450 admitted patients waiting on trolleys in University Hospital Limerick this month, making it the most overcrowded public acute hospital in the country.
The figures are from the Irish Nurses and Midwives Association who found there were not enough beds for 11,452 patients in hospitals in October.
The INMO said it was the worst-ever October for overcrowding and the second-worst month since records began in 2006.
The highest month on record is January 2018 when there were 12,395 admitted patients waiting for a bed.
The nurses and midwives' union has warned that patients are “at grave risk” because of overcrowding, together with chronic overcrowding.
After University Hospital Limerick, the most overcrowded hospitals in October were Cork University Hospital with 1,028 waiting and University Hospital Galway, which had 885.
An INMO analysis of HSE workforce figures shows that since the start of the year there are 308 fewer staff nurses, 37 fewer public health nurses and 87 fewer staff midwives.
It warns that understaffing is linked to higher patient mortality and longer stays in the hospital.
Labour TDs for the Mid-West region, Alan Kelly and Jan O'Sullivan said they knew that there were over 100 unfilled nursing posts in UHL alone.
“Staff at UHL are over-stretched and stressed beyond words because of the recruitment ban the Government continues to deny exists,” said Mr Kelly.
The TDs have called for a specially tailored plan for UHL that includes widening treatment pathways in Nenagh and Ennis general hospitals.
INMO general secretary, Phil Ní Sheaghdha, has warned that hospital overcrowding will worsen over the winter unless staffing became a “top priority” for the Government.
“Patients are paying the price for the HSE's 'go slow' recruitment freeze, which leaves many posts unfilled," she said.
Ms Ní Sheaghdha said she had sent a letter to the HSE to warn the health authority that its recruitment pause was putting lives at risk.
According to the INMO's Trolley Watch, University Hospital Limerick had the highest number of patients waiting for a bed on Thursday.
There were 59 patients waiting in UHL – 31 were in the emergency department and 15 were in wards elsewhere in the hospital.
Cork University Hospital had 52 waiting and University Hospital Galway had 46.
Altogether, there were 583 admitted patients waiting for a bed – 420 were waiting in EDs and 163 in wards.
According to the HSE's TrolleyGAR, there were 444 on trolleys in EDs on Thursday, with 245 waiting over nine hours and 79 waiting over 24 hours.
The health authority, which only counts the number of patients waiting on trolleys in EDs, found that the number had more than doubled compared to the same day last year when there were 209 waiting with 93 waiting over nine hours.