New Zealand First leader Winston Peters says there is nothing unusual about a non-disclosure document party board members are being asked to sign.
The document, in which board members agree to keep party business and membership confidential and not to talk to the media, also requires them not to associate with any other political party for three months after the next general election.
Peters said such agreements were common in every political party.
"Members who join the board are required to give an undertaking to keep the business confidential, there is nothing untoward in that at all."
He understood it had previously been in the nomination form but had been made into a separate document.