Business and Maori organisations are backing the call for a referendum on whether New Zealand should cut its ties with the Privy Council.
The Supreme Court Bill, now before Parliament, aims to end the relationship with the London-based final court of appeal and establish a local supreme court.
A group of fourbusiness organisations and one Maori body said such constitutional change should only be introduced following a three-quarters majority vote in Parliament or a referendum.
Business New Zealand, Federated Farmers, the Federation of Maori Authorities, the Institute of Chartered Accountants and the Business Roundtable said no attempt had been made to publicly discuss the issues involved and they feared "constitutional change by stealth could result".
The five bodies said the Privy Council provided "powerful protection against inconsistent judicial decision-making" in commercial cases and an objective consideration of Treaty of Waitangi issues for Maori.
They were concerned that the process for setting up a supreme court had begun without establishing any grounds for discarding the Privy Council.
Where they stand
* The Government needs support from other parties to pass the Supreme Court Bill.
* An inquiry into the bill by the justice and electoral committee has been widened after United Future said it might not support it if wider issues were not considered.
* National is opposed to replacing the Privy Council; NZ First and Act are organising a referendum to gain cross-party support to fight the legislation.