A female security guard has been attacked at Waikato Hospital and has been left with a suspected broken nose.
E tū union said the attack happened on Tuesday, when the guard was called to help with a highly agitated patient who was trying to leave the hospital.
It said the patient lashed out and punched the guard in the face, leaving her with a suspected broken nose.
Last month another female guard was assaulted and left with multiple facial fractures and was off work for at least three months.
There have been four serious assaults on Allied Security guards at the Waikato DHB and Canterbury DHB since Christmas.
E tū organiser Iriaka Rauhihi said another serious assault in just over a month at the same hospital was appalling.
"What are they waiting for - a fatality?" she said.
"Assaults are frequent at this DHB and we're well aware of Allied Security's record in Christchurch as well. Our members feel unsafe and I'm not the only one worried that someone will die if things don't improve - our members are saying the same thing."
The string of assaults raised serious alarm bells, E tū campaign lead Mat Danaher said.
"We are now looking at a record of failure to stem the ongoing violence on hospital wards in Waikato and Christchurch," he said.
He said DHBs were due to meet with E tū to review hospital security.
"There are systemic failures including under-staffing, lack of training and poor health and safety processes. We are looking forward to the upcoming security review and welcome the fact that DHBs nationally are taking this issue seriously."