Gambling reform campaigner Stephen Mayne has indicated he will preference the Greens above Labor, but Sex Party preferences - a potential key factor in the byelection - will favour Labor.

The first how-to-vote handouts have emerged, shedding light on preferences.

Labor appears to have snubbed Mr Mayne's overtures at a preference deal, placing him 12th on the how-to-vote guide.

Labor's cards ask voters to put Democrat David James Collyer second and Sex Party candidate Fiona Patten third.

Her party took more than 8 per cent of the vote in the 2012 Niddrie byelection but only 2.89 per cent in Melbourne in 2010.

She said Sex Party preferences could be the deciding factor in the election. The Greens preferenced Family First candidate Ashley Fenn last and are seventh on Labor's how-to-vote card.

Neither party's how-to-vote card places their lead rival last - the Greens have Labor's Jennifer Kanis ninth, while Labor gives the Greens' Cathy Oke 15th position.

Mr Mayne criticised the Labor how-to-vote card, saying it favours "the reactionary religious right" ahead of the Greens. "This is a progressive inner-city seat," Mr Mayne said. "They should change it [the card] ahead of election day."

Labor state secretary Noah Carroll said it was a "Melbourne Cup field" of candidates. "Our current how-to vote guide is seeking to maximise the Labor vote by designing it for ease of marking," he said.

He would not comment on the positions of the Sex Party, Family First and DLP.

Gerrit Hendrik Schorel-Hlavka, Joseph Toscano and Family First's Ashley Fenn were the only candidates to have registered how-to-vote cards with the VEC as MTW went to print.

Only VEC-registered cards can be handed out within 400 metres of a polling place on election day.

Source: Melbourne Times Weekly