Six prison guards at Paremoremo prison are in danger after a privacy breach put their personal details into the hands of violent inmates, says the Corrections Association.
Police have apologised and launched an internal investigation into how the information, including where the guards lived and the names of their partners, was handed to the inmates' defence lawyer.
The guards are witnesses at the upcoming trial of several inmates over an assault at Paremoremo prison late last year.
The Corrections Association said two of the officers were stabbed and needed hospital treatment.
Association president Alan Whitley told Morning Report the information should have been cut out of the disclosure documents.
The guards' safety and that of their families was compromised.
"We're pretty angry," he said.
"It's a situation that they shouldn't be in. Unfortunately it's not the first time this has happened, but we want to make sure this is the last time it happens."
Mr Whitley said the onus was on police to censor the details, but the defence lawyer should have exercised an ethical responsibility and removed them.
Waitemata district commander Superintendent Tusha Penny said police were discussing appropriate security measures for the affected staff members and their families.