The non-compulsory ballot, which runs until the end of October, will determine whether Australia becomes the 25th country to legalise same-sex marriage, while also healing a rift in the Government.
However, while Australia's biggest brands have pledged support for marriage equality, most have opted against public displays of support in the lead up to the public vote.
I will be voting "no" in the upcoming postal vote on same-sex marriage.
In April, Airbnb launched a campaign Until We All Belong, which called on the public to pledge support for marriage equality by wearing a ring designed by Marc Newsom.
The Australian Rugby Union (ARU) took a stance yesterday and joined the National Rugby League, Cricket Australia and the Football Federation of Australia...
"We proudly strive for these qualities in our own business and support these rights for all in society".More news: Moon rules out nuclear weapons in South Korea
Same-sex marriage advocates said they were disappointed the "divisive" postal vote will go ahead, but have vowed to campaign hard for a "yes" vote, buoyed by opinion polls showing the majority of Australians want marriage equality.
Nearly half of all Australians eligible to take part in the same-sex marriage postal survey will receive their ballots before the weekend.
"I wish to state quite clearly that the Catholic Church, through its official teaching, can not support proposals for the changing of the legal definition of marriage to include same-sex couples", he wrote.
The poll found 55% of the Cowper and Page electorates supported same-sex marriage.
The ballot of almost 16 million people at a cost A$122 million (S$133.86 million) will help Prime Minister Malcolm Turnbull unite his Liberal-National coalition, which had been fractured over the issue throughout his two-year tenure.
Labor lawmaker Penny Wong, who has children with her same-sex partner, told her party colleagues "hurtful and inaccurate" words had already been used. "But it provides limited protections", said Penny Wong, leader of the opposition in the senate. He pointed out that gay marriage had already been legalized in 23 countries and yet traditional marriage has not been undermined in those places.