The issue is a fault line running through Prime Minister Malcolm Turnbull's coalition and he's shied away from legislating during his two years in office even though he supports same-sex unions.
With companies such as Commonwealth Bank of Australia and Qantas Airways campaigning for the nation to catch up with New Zealand, the US and Britain, the postal vote is Turnbull's bid to break the deadlock. The Prime Minister says he'll urge his MPs to pass legislation by the end of the year if results due on November 15 show a majority support change.
"We said every Australian would have a say and we are delivering on that promise," Turnbull, 62, said at a "Yes" campaign event, urging both sides to argue their case respectfully. "Intolerant, disrespectful and strident voices undermine their own side of the debate."
Still, tensions are rising. Neo-Nazi groups have distributed homophobic posters in Melbourne. Prominent conservative MPs are urging people to vote against "political correctness," and are arguing that marriage equality could undermine family values and see radical sexuality and gender programmes rolled out in schools.
On the flip side, "yes" campaigners are being accused of intolerance for not respecting the right of people to vote "no".
"They've done everything trying to stop the Australian people from expressing their views on same-sex marriage," Lyle Shelton, a spokesman for the Australian Christian Lobby, said in an interview. He applauded the High Court's decision last week to allow the postal vote to go ahead, after same-sex marriage advocates tried to block it.
Tiernan Brady says he's seen negative campaigning against same-sex marriage before. He was the political director of the Irish "yes" side during its successful referendum campaign in 2015, and has been drafted in to lead Australia's equality campaign.
"In Ireland we faced a daily dose of red herrings" from anti-same-sex marriage campaigners, Brady said.
"They know the vast majority of Australians are for marriage equality so they're trying to change the debate through distractions and misleading. It's a disturbing attempt to create social division and we're determined not to fall for that. This has to be a united moment for the country, like it was in Ireland."
The "no" campaign may be gaining traction. Fifty-eight per cent of respondents supported changing the law in a Newgate Research poll released on September 9, down six percentage points from two weeks earlier.
The survey showed 31 per cent were against marriage equality, while only 65 per cent said they were very likely to vote. The poll of 800 voters had a 3.5 percentage point margin of error.
Turnbull's strong stance in support of the "yes" vote on Sunday came after he previously insisted he wouldn't be actively campaigning for it. The former banker has said same-sex marriage isn't a core issue and that Australians wanted him to instead focus on national security and economic growth.
That's been in stark contrast to Opposition Leader Bill Shorten, whose Labor Party is well ahead in opinion polls. Shorten has urged the Prime Minister to allow his MPs to hold a free vote in Parliament, without spending A$122 million on the postal vote.
"I hold you responsible for every hurtful bit of filth that this debate will unleash," Shorten, 50, told Turnbull in Parliament last month.
In Sydney, home to one of the world's biggest gay and lesbian Mardi Gras parades, Gardiner is wary about what the next two months will bring. Still, he's guardedly optimistic that he'll be allowed to marry his partner of six years by the time their second child is due in January.
"I didn't want this vote but if this is what we have to put up with to get marriage equality, we need to be as positive as possible," he said.
- Bloomberg
