A bookmaker that was offering odds on Australia's same-sex marriage postal survey has withdrawn the markets after a backlash from campaigners.

Sportsbet had several novelty options available on the survey, including "final result" and "number of Yes votes cast".

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The markets were criticised on social media, and by prominent Yes campaigner and Sydney MP Alex Greenwich, who described them as "a new low".

The online bookie had offered odds on same-sex marriage for about five years, but last night announced they would no longer take bets on the subject.

"Sportsbet respects that same-sex marriage is an important social issue," Sportsbet said in a statement.

"In response to recent views received regarding Sportsbet's same-sex marriage markets, we have decided to withdraw the markets."

Another Australian bookmaker, Crownbet, is offering markets on the survey and has been contacted for comment.

Mr Greenwich argued the mental health of LGBTI people had been affected by the debate, and that Sportsbet should donate any profits it made from the markets to charity.

NSW Greens MLC Justin Field tweeted his frustrations, saying: "Sportsbet should be ashamed of itself."

Last week, mental health service ReachOut said there had been a 20 per cent increase in people accessing LGBTI support services.

The Australian Bureau of Statistics has begun distributing forms to enrolled voters, with the result expected to be known in November.

The Coalition for Marriage did not respond to specific questions from the ABC about Sportsbet's markets, but did say: "The bigger gamble is that being pushed by the 'yes' campaign."