Michael Smith, the director of the Catholic agency for justice, peace and development, said that while some of the aims of a bill proposing contract management of prisons were good, the agency does not see privatisation as the only - or the best - solution to solving the problems expressed in the bill.
The Corrections (Contract Management of Prisons) Amendment Bill reflects the National-led Government's policy to allow the Corrections Department to tender and contract for prison management on a case-by-case basis.
The bill cites overseas literature claims that publicly delivered prison services can see a lack of incentives to innovate, take risks in delivery of programmes and be cost-effective.
Mr Smith agrees that there are "many aspects of state-controlled prison management that do need to change".
"We acknowledge that there are good reasons that groups from churches to Maori iwi and hapu are seeking more involvement in the care, rehabilitation and reintegration of prisoners both before and after release - and we strongly support these innovations.
"However, we believe such innovation is best achieved through partnership, rather than privatisation," he said.
Caritas acknowledged the bill is trying to make cost savings but one of the purposes of imprisonment is to provide opportunities for offenders to turn their lives around, and the success or failure of any prison service should be seen primarily in rates of re-offending after release.
Mr Smith said the "privatisation question needs to be addressed from the point of view of what is best for society as a whole".
Caritas research and advocacy co-ordinator Lisa Beech told the law and order select committee that "there are some powers of the state which are so significant and have such far-reaching implications for the protection of human rights that we need to think very carefully about contracting out those powers to any other hands".
That particularly applies wherever force or the threat of force is used, such as in the prison service.
Caritas cited some United States bishops' criticism of private prisons, arguing that when prisoners become units from which profits are derived, there is a tendency to see them as commodities, rather than as children of God.
The US bishops' view against private prisons hardened in 2003. As a result of increased violence in many privatised prisons, 43 bishops of southern states called for legislators to refuse to sign new contracts or renew existing ones with private prison corporations.