Canberra Health Services has maintained that "a clear threshold" had been breached by the nurse, and the drastic decision was part of the agreed processes in dealing with alleged misconduct.

The alleged major privacy breach, described by Canberra Health Services boss David Peffer as "a single one-off breach", is claimed to have exceeded the agreed privacy threshold and led to the senior nurse being stood down.

While details of the breach have not been revealed, it was understood to have been private medical information disclosed to an "industrial partner".

Mr Peffer said a number of staff across the health service had come forward after he sent an all-staff email about the original patient privacy breach. They reported instances where they thought they may have broken the rules. Health had identified one of those cases - the senior nurse - warranting investigation.

Health Services Minister Rachel Stephen-Smith said where there was a "health and safety risk", some information could be disclosed, such as in a child protection context.

"But the training that our health services staff receive is very clear around what types of circumstances might be exceptions in terms of that disclosure," she said.

"And obviously, Canberra Health Services has reached a position where [it has] concluded, in relation to this particular matter, that this was not one of those circumstances."

Mr Peffer stressed the breach involving the senior nurse was unrelated to the release of 13 patient records, sent to the ACT branch of the Australian Nursing and Midwifery Federation. One staff member has been sacked and two others have been stood down over these allegations.

However, the nurses' and midwives' union has defended the release of the medical records, arguing it had been done in accordance with exceptions in privacy laws.

The union's branch president, Matthew Daniel, has argued disclosures about patients' health information were lawful, saying it was a "complete surprise" when Canberra Health Services levelled accusations that patient privacy had breached.

Mr Daniel also said if nurses were guilty of unlawfully disclosing information, then so were bosses within Canberra Health Services, as they had disclosed patient information to the federation.

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The alleged breaches involving the 13 patients were committed by staff working in mental health and have been referred to the public sector standards commissioner.

Whole clinical records had allegedly been deliberately emailed outside of the organisation to an "industrial partner" over a period of years. Staff were advised of the breach in an all-staff email on March 6.

The latest leak was revealed publicly by The Canberra Times on Tuesday, more than a fortnight after Canberra Health Services staff were notified in an email and affected patients were told of the breach.

Canberra Health Services chief operating officer Cathie O'Neill said that people within the organisation could have discussions without breaching privacy threshold levels.

"All of our staff undergo mandatory training related to privacy and the specifics related to health record privacy," she said.

"All of our registered staff also undertake to adhere to their professional code of conduct, which also talks to maintaining patient privacy."

The decision to stand down the registered nurse has potential ramifications that could cascade into future award negotiations, although Ms O'Neill said she hoped the stand-down would not not adversely affect the management's ongoing relationship with the Australian Nursing and Midwifery Federation.

"We have requirements under our enterprise agreements that talk about how to manage alleged and then proven misconduct and so we have followed those processes," she said.

She said she "genuinely hoped" the relationship with the union had not been damaged by this incident.

"We continue to work with many members of the ANMF and have done so since this occurred; we will continue to do that in good faith," she said.

Mental Health Minister Emma Davidson told the Legislative Assembly on Thursday morning health records had been sent to the ACT branch of the Australian Nursing and Midwifery Federation from within Canberra Health Services.

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