Almost 10,000 patients went without a bed nationally last month.
The Irish Nurses and Midwives Organisation says it was the worst June on record for overcrowding.
University Hospital Limerick was the most overcrowded hospital while there was 1,059 patients without a bed at CUH, and 370 patients at the Mercy.
General Secretary of the INMO Phil Ní Sheaghda says she's worried for the coming months:
"Trolley count figures have been increasing and for this time of the year, they're very worrying because they're way higher than they should be. We know there's a couple of different contributing factors to that. What we're worried about is that there is a lack of determined action on behalf of the HSE to ensure that we remove the difficult working conditions that now exist for our members."
