More than 400 Christian leaders - including senior leaders of the Catholic, Anglican, and Methodist denominations in Aotearoa - have signed an open letter calling on MPs to vote down the Treaty Principles Bill.
The Bill, which has been championed by ACT leader David Seymour and will be considered by Cabinet on Monday, aims to redefine the principles of the Treaty of Waitangi.
ACT's coalition partners National and NZ First have both said they would not support it beyond its first reading.
The open letter, released on Monday by the organisation Common Grace Aotearoa, expressed the Christian leaders' opposition to the Bill and their commitment to Te Tiriti.
"We affirm that Te Tiriti o Waitangi protects the tino rangatiratanga of hapū and iwi. That rangatiratanga over land and taonga is to be upheld," it said.
"The proposed Bill is inconsistent with Te Tiriti o Waitangi in that it does not recognise the collective rights of iwi Māori or guarantee their relationship with the Crown. It would undermine what Te Tiriti guarantees, and what decades of law, jurisprudence and policy have sought to recognise."
Common Grace said Te Tiriti was a covenant between people.
"We believe God takes covenants seriously and that we are likewise called to honour our promises."
A "history of pain and promise" tied Christians to Te Tiriti, the organisation said in a statement.
"Christian missionaries were present at the signing at Waitangi, then carried the Treaty sheets to other rangatira around the country. This connection motivates Christian leaders to speak up today."
Among the signatories were Commissioner Mark Campbell, the Salvation Army's territorial leader of New Zealand, Fiji, Tonga and Samoa; the Very Reverend Jay Ruka, Dean of Taranaki Cathedral; theologian and historian Dr Alistair Reese, who gave the homily at this year's Waitangi dawn service; and Dr Alan Jamieson, the general director of Arotahi (the New Zealand Baptist Missionary Society).
Baptist pastor Helen Bereton said religious freedom was granted in the fourth oral article of Te Tiriti.
"As a religious person and a religious leader, I decry efforts to undermine Te Tiriti and support any efforts that promote the furtherance of genuine, life affirming, and mutually beneficial biculturalism in our nation."
Ruka, an author of a book about Te Tiriti and Christianity, Huia Come Home, said the Bill was "holding our nation in contempt".
"It is beyond grievous that David Seymour is intentionally pitching the sacredness of Te Tiriti O Waitangi and the significance of democracy against each other. He is tricking New Zealanders into thinking that to honour our founding contract is to demerit democratic representation. This is a lie.
"As a Christian leader, I steadfastly oppose this falsity."
Common Grace said the leaders would continue to speak out to uphold the mana of Te Tiriti.