The Sensible Sentencing Trust has been branded "loopy" by the Justice Minister.
Andrew Little told NZME he hasn't met with the hardline group all year.
"I have a problem specifically with Garth McVicar, who has a bit of a track record of what I think are some pretty loopy views," he said.
In particular, Mr Little cited Mr McVicar's support for a man who stabbed a teenager to death, his comments that letting gay people marry would increase crime, and his congratulations to the police when they shot a man dead.
Mr Little, who wants to reduce New Zealand's prison population, also told NZME he has a problem with David Garrett - the disgraced former ACT MP who now works with the Sensible Sentencing Trust.
Earlier this month Mr Garrett wrote in a guest post for right-wing website Kiwiblog that "no one with half a brain" cares about violent prisoners who commit suicide.
"That's not a set of values that I want to be anywhere the debate about reforming our criminal justice system," said Mr Little.
A senior figure in the Sensible Sentencing Trust, Scott Guthrie, has recently quit the group, saying he no longer believes their hardline approach works.
Mr McVicar unsuccessfully stood for Parliament with the Conservative Party in 2014. In 2017 he blamed "Māoridom failing their kids" for New Zealand's growing population, now at a record high.