Several ambulances where held up outside the Mater for over an hour this week.
The scene has been described as on the brink of chaos.
It's understood the ambulances were delayed due to a lack of trolleys available for patients in the hospitals emergency department.
When this happens it means that ambulances have to wait to get their trolleys back before they can go on another call.
Up to eight ambulances were pictured outside the Mater on Tuesday afternoon.
The nurses organisation says that 26 patients were waiting on trolleys that day while the Mater says there was an exceptional number of admissions in the past two days increasing ambulance turnaround times.
There's now calls on the Health Minister to address this ongoing problem.
