A parliamentary select committee has been told that private management of prisons will mean less accountability, reduced services and increased costs.
The Public Service Associaton and the Council of Trade Unions presented their submissions to the law and order select committee on Wednesday.
The committee is considering a bill allowing prisons to be managed privately.
The PSA surveyed its 2500 members who work for the Corrections Department and told the committee 89% felt privatising prison management would have a negative impact.
The CTU maintains it is incorrect to say that privatisation delivers genuine cost savings, unless conditions are completely run down for both workers and prisoners.
It says overseas research shows public run prisons are better run in terms of quality and value.