A Maori tikanga expert says the impact on prisoners who have their taonga taken from them could be devastating.
From next week, the Department of Corrections will ban pounamu and manaia taonga (pendants) for new inmates.
Inmates who have taonga can keep them but items from prisoners transferred to other facilities will be sent back to their whanau.
Pou Temara, a professor of culture and Maori language at the University of Waikato, said taonga are often family heirlooms.
He said the mauri, or essence, of those who have worn the item is transferred to the wearer, making it very significant.
Pounamu often went through several hands and many hours' work before it was presented as a gift, he said.
The Department of Corrections said pounamu and manaia were items of desire and value which could be illegally bartered in prison. The precious items could also get lost in jail and the policy would remove that risk.
But Maori Party leader co-leader Te Ururoa Flavell said the ban was over the top and went too far and he had asked for an explanation from Corrections Minister Sam Lotu-Iinga.
"I think it's going a little bit too far, and a little bit over the top, unless we have some clear evidence around the issues that have been raised," he said.
"For Maori, that taonga that they have are things that they hold dear to themselves. For them to be taken off is pretty serious."