An open letter by 13 academics and lawyers says Te Ture Whenua Māori Bill has been rushed through Parliament and urges the Prime Minister to stop it.
Māori Development Minister Te Ururoa Flavell said the Bill would give Māori landowners greater autonomy, better protection under the law and more support to develop the land if that is what the owners want.
But it has been criticised by Labour, who called it dysfunctional, and New Zealand First, who said it was elitist and would disadvantage Māori. Mana Party leader Hone Harawira said the bill was a "poisonous and destructive cancer".
In the open letter sent by the group today, they said the reform process had been too quick and had created confusion.
They said they believed it was an important area of law and policy and should not be rushed.
Professor Jacinta Ruru from the Faculty of Law at the University of Otago - who signed the letter - said they welcomed the attention on Māori land, but were not convinced a new law was needed.
"We wrote the letter because we are really concerned about how rushed this process has been and we are cautioning the government not to proceed with enacting this bill until we've had the opportunity to more fully consider that this is the right reform for Māori land."
Ms Ruru said she was concerned the bill, which had taken more than 30 months to put together and had involved 16 drafts, would take months to understand.
"The current bill is over 400 pages long and is recognised by lawyers throughout the country that is going to take us a significant amount of time and investment to fully understand where the current bill is at."
She said this was an enormous change to existing law and even the National-led select committee said in the majority the new law would need an 18 months lead-in time.
"This is entirely a new way to approach Māori land and we're not convinced that there has been the evidence to prove that this is the right approach.
"We can certainly be looking at the current law and how to make it better but to completely start again to move away more than 100 years of jurisprudence through our Māori land court to be replaced by a new Māori land service that we have very little information about.
"We still don't understand how exactly it's going to be resourced and what it is going to deliver to Māori land owners."
The letter was signed by Tavake Barron Afeaki, Kerensa Johnston, Leo Watson, Dr Robert Joseph, Dr Valmaine Toki, Aidan Warren, Dr Paerau Warbrick, Neuton Lambert, Rebekah Jordan, Dr Carwyn Jones, Annette Sykes and Angeline Greensill