Videos revealing an inmate "fight club" must be investigated independently at once, the Corrections Association president says.
Beven Hanlon said prison staff were frequently attacked at privately-run Mt Eden jail.
His comment came after footage emerged on YouTube showing gang members engaging in one-on-one fights at Mt Eden as other prisoners cheered them on.
Private firm Serco runs the prison on a contract from the Department of Corrections.
The fight club videos have sparked calls for Serco and Corrections to be investigated.