The National Iwi Chairs Forum and the Pou Tangata Iwi Leaders Group are united against the proposed repeal of Section 7AA of the Oranga Tamariki Act.
The controversial Oranga Tamariki (Repeal of Section 7AA) Amendment Bill was introduced to Parliament this week.
Section 7AA is a mechanism to give effect to Te Tiriti o Waitangi and to the establishment of partnerships between Oranga Tamariki and iwi and Māori organisations.
Children's Minister Karen Chhour earlier told RNZ that she wanted Oranga Tamariki to continue its partnerships with iwi and Māori groups.
But Iwi Leaders Group lead advisor Robyn Rauna said if that was the case, section 7AA should be left in the legislation.
It was an enabler of relationships with iwi and without it Māori would be completely reliant on Oranga Tamariki's discretion, she said.
"Numerous reports have shown inadequacy around the care and protection of mokopuna and tamariki, what do our mokopuna, tamariki have to go forward? Not a lot at the moment.
"And the minister has not invited iwi Māori to look at a way to co-design this framework that she's talking about, at the moment it's all talk."
Chhour said since section 7AA's introduction, Oranga Tamariki had the highest level of harm in return-to-home placement since recording began.
But Rauna said the forum had not seen evidence of that in its work with iwi across the country. In fact, it had seen improving outcomes for tamariki.
The forum was hugely disappointed by the proposed bill, particularly off the back of the efforts of iwi groups and the Māori Women's Welfare League in taking an urgent claim to the Waitangi Tribunal, Rauna said.
"[We are] really disappointed that in order to circumvent an inquiry into these matters the bill was then introduced."
The forum made the minister aware of the concerns that iwi leaders around the country had about the bill, she said.
The proposed repeal would be a significant setback in the progress towards genuine partnership and collaboration between the Crown and Māori, she said.
"The request to remove 7AA didn't come from us, it only came from one party and one party alone... and I'm speaking specifically about the ACT Party."