Green Party MP Keith Locke is close to completing his private member's bill seeking a referendum on whether New Zealand should replace the monarchy.
Mr Locke said yesterday he had been working on the legislation for "months". It was coincidence he was likely to complete it so close to the Queen's visit, he told National Radio.
The Queen and the Duke of Edinburgh are due to arrive tomorrow.
Mr Locke said the monarchy did not reflect New Zealand's independent, multicultural nature.
Private member's bills are drawn from a ballot to be debated every second Wednesday.
If enacted, the bill would allow New Zealanders to decide if they wanted the monarchy. It would also discuss whether the new head of state should be elected, or chosen by 75 per cent of Parliament.
Monarchist League of New Zealand spokesman Noel Cox said he had no objection to a referendum, but republicans had so far failed to justify the need for a change.