The Health Information and Quality Authority has said it continues to be concerned that Tallaght Hospital is not effectively managing the risks to patients requiring acute admission.
HIQA said it 'believes that this poses a serious risk to these types of patients'.
Members of the Tallaght Hospital Action Group were due to meet Minister for Health James Reilly at Leinster House this afternoon.
Richie O'Reilly from the group says it has been warning for years that the number of people going through the emergency department is above capacity, while the budget for the hospital has decreased.
He said the hospital is designed to cater for 350,000 people, but is dealing with 530,000.
Meanwhile, HIQA has published the terms of reference for its statutory inquiry into the safety and governance of care at the hospital's emergency department.
Under the eight terms of reference, the inquiry will assess the quality, safety and governance, and accountability for services provided to patients who attend the emergency department.
It will examine if the board of the hospital has been effective in managing risks to patients.
Specific patient cases will be incorporated into the inquiry where appropriate.
The inquiry will examine the patient journey from initial assessment, through admission to discharge, as well as the corporate and clinical governance.
The membership of the inquiry team will be announced shortly.
HIQA announced an inquiry last Saturday.
It followed remarks at an inquest by Dublin County Coroner Dr Kieran Geraghty, who said the emergency department sounded like a very dangerous place.
The inquest was into the death of 65-year-old Thomas Walsh from Kilnamanagh in Tallaght in March at the hospital.
He had been moved away from the emergency department to a so-called 'virtual ward', a corridor area with no oxygen, monitors or equipment.
It has also emerged that last year in the emergency department a patient suffered a cardiac arrest on a chair while awaiting admission.
According to a written report from the hospital's emergency department consultant Dr James Gray to the inquest, the hospital has had up to 56 patients placed in such 'grossly unacceptable' conditions.
Three TB cases were also put on the corridor in recent months, prompting an infection risk.
Dr Gray said he had profound concern that in the future there may be another cardio-respiratory arrest should the status quo remain.
He said that he and colleagues had raised their concerns with the Medical Council, Amnesty Ireland and the Ombudsman.
Dr Gray has called for a total and immediate ban on the use of the corridor.