New Zealand Nurses Organisation Bay of Plenty organiser Angela Neil said the union was worried about the potential cut "because that affects our members and the safety of our nurses".
"We understand from talking to our members that it will be evening security staff."
The rate of assaults of staff at Tauranga Hospital has steadily increased in recent years, with reported cases of violence and aggressive behaviour at the hospital rising from 53 in 2008 to 205 in 2010.
In 2010, staff were assaulted 75 times and police were called to 100 incidents.
Ms Neil said security officers often walked patients and staff to their cars at night and ensured no suspicious people were wandering around the hospital.
She questioned who would do the work.
"It's not just nurses. It's everybody. We are very concerned."
Hospital staff, who spoke on the condition of anonymity, said there were major concerns that staff inexperienced in security, such as nurses, orderlies and cleaners, would be forced into dangerous situations.
Jamie Toko, organiser for the Bay of Plenty branch of the Service and Food Workers Union, which includes orderlies, said it was unacceptable that the health board expected to scrimp on security.
"If the DHB did that, patients are going to be at risk. The guards are going to be at risk themselves."
Ms Toko said staff safety outweighed the money expected to be saved under the proposal.
The health board confirmed it was reviewing security services at the hospital and proposed to disestablish at least one position.
The final decision will be announced to affected staff on May 25.
Board chief operating officer Phillip Balmer would not say how much money was expected to be saved but said the purpose of the review was to assess whether staffing levels met the hospital's safety requirements.
"We will not be making any comment on the review of the security service ..."
Tauranga man Andy Turner, whose son is a patient at the hospital, said the concerns were a "fair call".
"Obviously, you would like to think there were the necessary precautions in place to make sure they [staff] were looked after," he said.
"The other side of it is some of the access to drugs and other stuff that's on site and could make this place a little bit of a target."