A Corrections lobby group is against a bill proposing a compulsaory prison sentence for those with three convictions for violent crime.
The Sentencing and Parole Reform Bill would impose a minimum sentence of 25 years in prison without parole on anyone convicted of a third violent crime.
Rethinking Crime and Punishment director Kim Workman says 16,000 offenders have been convicted of three or more such crimes since 1980.
He says 2000 are in prison and claims that jailing most of the others would require about 45 new prisons at a cost of $7.5 billion.
Mr Workman says many offenders commit violent crimes between ages of 18 and 25, but claims they will stop after reaching their 30s.
He says there is no point paying money to keep someone in jail for 25 years if they are at the end of their criminal career.
