Christian organisation Prison Fellowship says it is racing to make changes to the faith-based unit at Rimutaka Prison to prevent it being shut down by the Corrections Department.
An evaluation last year said reoffending rates for inmates in the unit were not substantially different compared to others.
The director of Prison Fellowship, Robin Gunston, says he has questions about the methods used in that evaluation, but says staff are still making changes, including to the criteria for entry to the unit.
He says Corrections has issued additional requirements in the past two weeks, which must be met by the end of May.
Mr Gunston says the unit was already changing lives and helping inmates face the reasons for their offending.