Green Party Justice spokeswoman Golriz Ghahraman will try to amend the Government's repeal of the Three Strikes law to allow prisoners currently serving time under the legislation to have their sentences re-examined and potentially shortened.

Her amendment, were it to be successful, could mean some prisoners being released after serving less time than their current sentence - although this is not guaranteed.

Labour MPs sitting on the select committee examining the bill were unmoved by a push to re-examine sentences.

Ghahraman said Labour's apparent unwillingness to move the issue was evidence of its fears about being made to look "soft on crime".

"Fear mongering has come into the apparatus in New Zealand," Ghahraman said.

"The opposition have been very willing to make political football out of law and order reform - that 'tough on crime' rhetoric in an emotive non-evidence-based way," she said.

Three Strikes was an Act Party creation from 2010 when the party was supporting a National-led government.

The legislation imposes progressively harsher penalties for each "strike" offence committed.

By the final "strike", the maximum applicable penalty without parole must be imposed, unless the court considers it would be manifestly unjust to do so.

National's Justice spokesman Paul Goldsmith said his party would not be backing any such amendment, and that it opposed the repeal of Three Strikes.

Green Justice spokeswoman Golriz Ghahraman wants to legislate a regime for reopening Three Strikes sentences. Photo / Mark Mitchell

"People were sentenced under the law that existed at the time - so there would be no good argument to reopen all that and it would be a strange priority," Goldsmith said.

"The Government thinks we're too tough on the most serious criminals. It's a very odd conclusion to draw given the state of things at the moment," he said.

Labour introduced legislation to repeal the Three Strikes legislation, which recently returned from the Justice Select Committee. It is currently awaiting its second reading.

One question left unanswered in the repeal bill was what to do with prisoners who had been sentenced under the Three Strikes regime and who were serving sentences that would be longer than what they would have served had the legislation not been in place.

Officials, in a regulatory impact assessment, had pondered ways of reassessing sentences and bringing them into line with the new sentencing regime, but these were not in the legislation as it was introduced to Parliament.

Justice Minister Kris Faafoi wrote to the Justice Select Committee, which was examining the bill, and asked it to consider whether a regime of reassessing sentences could be included in the legislation.

The committee decided not to recommend any change that would include a regime for reassessing sentences.

"We have considered this option and we do not wish to recommend any changes to the
bill of this nature.

"Retrospectively changing sentences would require complex approaches that would differ depending on which of the affected groups were included," the committee said.

The committee also said it risked affecting victims of crimes committed by Three Strikes offenders.

"Retrospectively reducing sentences or allowing parole would significantly affect the victims of those offenders, who could not have expected any re-sentencing or parole hearings to occur," the committee said.

Ghahraman will put up an amendment at Committee of the Whole House stage in a last-ditch attempt to legislate a regime for reassessing sentences. It will need Labour support to pass, and this is unlikely given it was the Justice Committee's Labour majority that was behind that committee not recommending any changes to the legislation.

Ghahraman said that so few people were serving time under Three Strikes that any regime would only impact a small number of people.

"The criminal justice sector started to resist this law. Prosecutors and judges started to deal with cases differently so they didn't have to trigger the three strikes law," Ghahraman said.

"Anyone who did get [sentenced] falls into a very unlucky category of people who probably got sentenced early on," she said.

She said sentencing should "go back to first principles", which are "what is best in each case to ensure public safety and rehabilitation and successful reintegration into the community".

"Three strikes took away that discretion completely from the people who deal with thousands of cases per year - probations, police, Crown prosecutors, defence lawyers, and judges lost the ability to have that discussion and come up with the outcome that would best serve the community," Ghahraman said.

She said any regime to reassess sentences would not automatically mean they would be released early. Instead, they would be re-sentenced based on current sentencing guidelines, not Three Strikes.

"Anyone who is calling for those cases to be reconsidered is not calling for a shortening of that sentence per se but for consideration for what is best for community safety and rehabilitation in that person's case," Ghahraman said.

She said that any retrospective regime could shorten sentences, but not lengthen them.

"The principle of legality says that you can't retrospectively legislate to take away someone's rights or interests, but you can retrospectively legislate to give someone their rights or some benefit - so you'd have to legislate in a way that means their sentences can't be raised," Ghahraman said.

She noted the Government had expunged historic homosexual convictions in recognition of the fact the Government had changed the law in 1986 to decriminalise homosexuality.

The regulatory impact assessment on the repeal bill said harsher sentences tended not to deter crime.

"The severity of punishment has essentially no deterrent effect," the paper said, adding that the "certainty of apprehension has a small deterrent effect", but this was mainly for white collar offences.