The Irish Penal Reform Trust has said plans around minimum tariffs for life sentences is 'putting the cart before the horse'.
Justice Minister Helen McEntee has revealed that judges will be able to set minimum sentences of up to 30 years for the most serious crimes.
As part of the plans set to be brought forward in the coming weeks, she also she wants fewer petty offenders to go to prison.
Saoirse Brady is executive director of the Irish Penal Reform Trust.
She told Newstalk Breakfast prison should not just be about punishment.
"A person who is serving a life sentence will know that they will at least be serving 12 years.
"On top of that I suppose they don't know how long they might serve, so this might bring about some certainty both for victims and for the person in prison themself.
"But what I would say is we're putting the cart before the horse a little bit here.
"We have to go back to what the purpose of sentencing is; and IPRT would really welcome a wider public debate on sentencing.
"But we need principles for sentencing.
"Sentencing is about punishments sometimes, it is about deterrents, but it's also about reform and rehabilitation.
"And we know that people can and do change - we see progress that is made by people in prison.
"So we would need to build in reviews for that progress, I think".
But she said they do welcome proposals around community sentences for petty crimes.
"What we very often see are people going in to prison for 12 months or less, when maybe that isn't proportionate or the appropriate response.
"Very often we know that people who end up in prison have social issues - they're ending up there because of homelessness, mental health issues, addiction.
"And we need to really have wraparound services for them and allow them to serve their sentence in the community.
"It's actually not just beneficial for the person themselves... it's more cost-effective for the taxpayer.
"A prison space costs around €80,000, a community supervision order will cost in the region of €6,000 or less".