Two security guards at Middlemore Hospital were stabbed on May 21 after a scuffle between a staff member and another person.
One of the guards suffered stab wounds to the hand, while the other was stabbed in the back of the neck.
E tū Union director Sam Jones said they were stabbed with a pair of scissors when they intervened in the attack on a health care assistant last month.
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E tū delegate Gareth Liley was one of the guards who was stabbed and said it wasn't the first time workers had been injured on the job.
"We have been warning the DHB of the risk of something like this happening. We want to go home safely to our families, just like everyone else does.
"What we need is the right support, personal protective equipment, staffing levels, and training, to ensure we can keep ourselves and our colleagues safe at work."
E tū is now calling for a serious harm investigation into what happened.
Jones said the union had demanded an improvement in working conditions at Counties Manukau District Health Board and that WorkSafe be notified to conduct a serious harm investigation into the incident, with worker representation.
"It appears that despite the stabbings, because no one was in hospital overnight, they don't see it as serious enough. It's just unacceptable.
"Violence in the workplace cannot be treated by our health system like business as usual for our essential service workers."
Bringing in standardised training, pay rates and hours, appropriate PPE, staffing levels and personal support at all DHBs would go a long way to helping the situation, he said.
They were all recommendations included in a March 2020 report on New Zealand's hospital security services by the National Bipartite Action Group.
It found that during a 12-month period, there were more than 5000 security incidents, including 230 reported assaults, logged across 13 of 20 DHBs.
Respondents also agreed the number and frequency of acts of aggression in hospitals was on the rise.
Jones said the review was an important piece of work and a good example of health unions and the DHBs working collaboratively to find solutions to an increasingly serious problem across our hospitals.
"We see the recommendations and their integration into the workplace as a crucial step in keeping our frontline health workers and patients safe."
A spokeswoman for the Counties Manukau DHB said the incident took place at 4.45pm on May 22, but didn't confirm if police were contacted or investigating.
"Staff members were treated for injuries and are receiving support.
"CM Health takes the health and safety of staff seriously and has zero tolerance for any inappropriate behaviour toward our staff. Health and safety and clinical reviews will occur. We can confirm WorkSafe was notified of the incident."