Government officials say the mail-in poll will cost about 97 million US dollars.
Hinkler MP Keith Pitt, who does not support same-sex marriage, is urging all voters to have their say in the postal survey.
While not legally binding, if the survey shows a majority favor same-sex marriage, a bill legalizing same-sex marriages would be introduced in parliament, where members of parliament would not be bound to vote with the public.
Pastor Brad Chilcott, from the Pentecostal Activate Church in Adelaide, said the church's involvement in gay conversion therapy is "cause for shame and repentance".
"This bill can not stop all of the hurt, all of the prejudice that is being expressed, all of the lack of acceptance that is being communicated to LGBTI Australians, to same-sex couple families".
In a decision lasting only minutes, High Court Chief Justice Susan Kiefel??? dismissed the plaintiffs' challenges, and ordered them to pay costs.
If the postal survey finds most Australians want gay marriage, the Parliament will vote by December on legislation to lift the prohibition on gay marriage. "Mr Shelton is the identified public leader of the 'no" campaign.
Prolific Perera helps World XI set up Pakistan decider
Yesterday, Pakistan beat the World XI by 20 runs in an exciting finish, celebrating the return of global cricket to the country. It was left to Ahmed Shehzad and Babar Azam to fix the innings, like they did with their 122-run stand on Tuesday.
Despite earlier reports, Senator Cormann said he was not aware of any gag order on Cabinet ministers, indicating they would be free to campaign as forcefully as they wished for either side. "Please don't leave this change to other people".
IT'S a simple question but one that will have far-reaching consequences: should the law be changed to allow same-sex couples to marry?
He said Australians were "absolutely able" to conduct the debate respectfully. "We are absolutely committed to legislating for marriage equality", he said.
Meanwhile, Prime Minister Malcolm Turnbull has come out in support for the "yes" campaign at an event in Sydney on September 10.
Christians who support same-sex marriage have hit back at prominent "no" campaigner, Australian Christian Lobby managing director Lyle Shelton, over his comments that parents should have the right to send their kids to gay conversion therapy.
"We want this process to be fair and for Australians to get the opportunity to have their say in an appropriate environment", Finance Minister Mathias Cormann said.