Members have reported delays in more than 15 hospitals
SIPTU members in the National Ambulance Service (NAS) have expressed concern over the impact of the trolley crisis on its services.
They say they are experiencing delays in signing patients into emergency departments in hospitals across the country.
Members have reported such delays in more than 15 hospitals.
The hospitals affected include Letterkenny, Waterford, Our Lady of Lourdes in Drogheda and St Vincent's in Dublin.
SIPTU health division organiser, Paul Bell, said: "Prior to the current crisis, the time that patients were spending between arriving at a hospital and being transferred from the care of ambulance staff to that of the emergency department team was on average 20 minutes or less.
"However, due to the current overcrowding crisis in emergency departments this time has increased to on average between one to three hours in many hospitals across the country."
He adds that such delays are having "knock on effects" on other ambulance services - including responding to emergency calls and routine patient transfers.
"The Minister for Health, Simon Harris, must contact HIQA, the regulator of the NAS, to fully brief it on the impact that the emergency department crisis is having on our members' ability to comply with guidelines in relation to ambulance response times", he added.
SIPTU say workers in the NAS are "increasingly disturbed and frustrated" by the impact that the ongoing crisis in hospital emergency departments is having.
The warning comes as figures show the number of people on trolleys in hospitals around the country is at 602.
That represents a drop of just 10 people since Tuesday.