A conservative religious group is thought to be behind the leaflets slamming the policies of Labour and the Greens.
Two smear mail-outs have already surfaced this week, one calling Labour's health policies an "uncaring legacy" with an agenda including legislation that would "see men in dresses and male transvestites in women's toilets". The other takes aim at the Green Party - Labour's likely coalition partner.
Deputy Prime Minister Michael Cullen said there was a "pretty dirty campaign" afoot. "It seems pretty obvious a National Party front organisation is being used."
But now the attention has turned to the Exclusive Brethren after One News tracked the names on the leaflets and found the authors are all members of the 300-year-old conservative religious group.
Greens' co-leader Jeanette Fitzsimons said she was "quite surprised" the Christian group is behind the leaflet drops. "The Exclusive Brethren say they have no involvement in politics at all and don't vote."
Stephen Myles Win of Mangere was behind the first mail-drop, slamming the Green Party. A copy of the Exclusive Brethren's private address book obtained by One News shows a Mr Myles Win and his wife Mary who reside at an Auckland address is the same name and address printed on the leaflet.
Myles and Mary Win also feature on an anti-Labour, pro-National letter sent out last month. The co-author of that letter, Milton and Michelle How of Rangiora, north of Christchurch are also listed in the Exclusive Brethren address book.
And J Hawkins whose Christchurch address was printed on an anti-Labour pamphlet, has his home listed in the address book but at a different location.
The Exclusive Brethren are a very conservative patriarchal religious sect who only marry within their community, don't allow women to wear make-up and don't use the internet or watch television. A leader of the Exclusive Brethren refused to comment.
More leaflets are set to hit letterboxes later this week. The Business Printing Group in Auckland said it is printing two or three similar leaflets that will be ready this week but refuses to comment further. The Greens have already complained to the Chief Electoral Office.
Helen Clark is calling the Brethren's involvement a very strange turn of events. "I wonder if their members even know because the Brethren have always said that they don't get involved in politics."
And the National Party continues to distance itself from the leaflets.
While Exclusive Brethren members refuse to vote, they have been involved in politics overseas. Last year a group of Exclusive Brethren businessmen spent nearly $750,000 supporting the re-election of US president George Bush.