Opposition parties are trying to force the Government to hold a referendum on its plan to scrap links to the Privy Council.
Legislation is already before Parliament to cut ties with the final court of appeal in London and establish a local Supreme Court.
Act and New Zealand First yesterday said theywere organising a referendum and working to gain cross-party support to fight the legislation.
New Zealand First leader Winston Peters said the question was too big for party politics and for politicians.
He was organising a petition to ensure a referendum is held.
To trigger a non-binding referendum, the Clerk's Office in Parliament must be satisfied that 10 per cent of registered voters (about 265,000) have signed a petition for it.
Mr Peters has 12 months to gather the signatures.
"New Zealand First has invited other political parties to put their names to the petition and to activate New Zealanders of all persuasions to sign the petition and participate in the referendum," he said.
Act justice spokesman Stephen Franks yesterday wrote to all political parties asking for support for a citizens' initiated referendum on the issue.
National's justice spokesman, Richard Worth, said his colleagues backed the call for cross-party support.
The Government needs support from other parties to pass the law. The Greens are still considering their stance.
