Wait times for patients in need of urgent treatment at Canberra's emergency departments are now the worst in the country, according to the Australian Institute for Health and Welfare.

One staff member has described the tension in the department as "thick" and said the public were becoming more frustrated due to a "bombardment of patients" attending.

An ACT Health spokesman denied any suggestion staff were working in violation of their enterprise agreement but acknowledged many were working overtime to meet the demands of patients.

"As with other parts of the hospital some staff have agreed to do overtime shifts," he said.

"ACT Health has recently completed a recruitment process for more staff in the emergency department. This will help reduce the need for overtime shifts."

Australian Nursing and Midwifery Federation ACT secretary Jenny Miragaya said a number of staff had resigned in recent months with reinforcements eagerly awaited.

Opposition Leader Jeremy Hanson said he was "very concerned" about staff morale in the emergency department and called on the government to ensure staffing levels were adequate.

"I call on the government to make staff at the emergency department their number one priority as they are some of the hardest working and most important people in Canberra," he said.

"If staff are having to work overtime to fill gaps and shortages then that is not sustainable over the long term."

According to the AIHE, just 50 per cent of urgent patients were treated within 30 minutes with 61 per cent of all patients seen within two hours.

In July, emergency department nurses called for indemnity amid fears they may be forced to breach professional standards by seeing most patients based on waiting time, not need.

Staffing concerns come as management move to keep coffee and tea supplies under lock and key during business hours due to budget restrictions and suspicions of theft.

Coffee and tea have been provided to patients and family members for many years, with emergency department staff also granted access given their working conditions.

An email sent by hospital management said they suspected staff from other wards had been helping themselves to supplies reserved for patients and emergency department workers.

"This is a privilege and not a standard practice offered to all staff across Canberra Hospital and Health Services," the email said.

"There is a possibility that our supplies are being taken from other hospital departments and therefore, we are locking the supply cupboard so that we can monitor how much stock we as a department are using."

The emergency department exceeded its budget for food and beverages last year and management warned staff it was likely to do so again unless changes were made.

During business hours on Monday to Friday, emergency department staff will have to contact the director's personal assistant who will unlock a supply cupboard containing the coffee and tea.

"On Friday evenings, the pantries will all be fully stocked and additional box of tea, coffee and sugar will be placed in the acute kitchenette area," the letter said. "This will last the weekend."

An ACT Health spokesman said coffee and tea was not being removed from the department but its usage would be monitored to ensure it was available to families and carers.