Labour leader Phil Goff says the Government should consult the Opposition about the scope of an inquiry into New Zealand's constitutional arrangements.
The Government agreed to a constitutional review as part of its support arrangement with the Maori Party. Terms of reference for the review are expected to be released in the next few weeks.
Mr Goff says constitutional issues should be decided on a cross-party basis.
"So far there's been no effort by the Government to get in touch with us to discuss those issues," he says.
"If the Government's planning a constitutional review from a partisan basis, then they've got it wrong from the start. I would expect Labour, the Greens and other parties all to be involved."
It won't be rushed, says PM
Calling the review a "long conversation", Prime Minister John Key says it will not be rushed. It will be a lengthy process, he says, that could run until 2012 or 2013, and any significant recommendations - about the length of the parliamentary term, for example - would then have to go to a referendum.
Mr Key says no decision has been made on when parties will be consulted.