The words "Vote No" appeared in the sky as competing campaigns seek to shore support for the "right" answer to the question -- "Should the law be changed to allow same-sex couples to marry?"
No one has claimed responsibility for the skywriting, which some locals -- yes voters -- say was an offensive intrusion into their Sunday.
Journalist Shane Bazzi was walking with his boyfriend in the Sydney suburb of La Perouse when he noticed the skywriting. "Thanks for ruining my Sunday morning," he said on Twitter
as he shared a picture of the message.
Bazzi told CNN the skywriting was a "hurtful" reminder of Prime Minister Malcolm Turnbull's decision to subject LGBTQ Australians to a "hate campaign" by putting the matter to a survey rather than a vote in Parliament.
"We can't escape it. Our lives now being debated in the sky. We can't even look at the sky without being told we don't deserve equal rights," Bazzi told CNN.
Same-sex marriage advocates had tried to stop the vote partly because it would give opponents a platform to promote intolerant and hurtful messages to a national audience. However, a court ruled it could go ahead.
Last week, the Australian government sought to address concerns by passing new temporary laws banning hate speech for the duration of the vote. The new law threatens a $12,600 ($10,000) fine for people who vilify, intimidate or threaten harm "on the basis of sexual orientation, gender identity, intersex status or religion."
The postal vote is voluntary and non-binding, meaning the government is not legally obligated to go along with it. If Australians vote in favor, Parliament still would have to pass legislation to make same-sex marriage law. The results will be announced on November 15.
From a Newtown pub, Michael Beveridge took a picture of the skywriting as it began to dissipate in the wind. At first, he made light of it by imagining how much money was paid to broadcast a temporary message. Then, he thought about the potential reach of the message.
"I was just bloody dumbfounded -- it was just such an old fashioned, super-villain way of promoting inequality and hatred," he said in an email to CNN.
"At first, I laughed and hoped the company that did it went bankrupt but then I realized that literally anyone within a 10-mile radius could see the writing," he said. "Being told you're not worthy while you're eating your bacon and eggs just seems like a pretty devastating way to start your Sunday."
"No" voters noticed the skywriting, too, and endorsed the message on social media. They were far outnumbered by critics.
The skywriting appeared the morning after the Coalition for Marriage
kicked off a campaign against changes to the Marriage Act Saturday at the Sydney Convention Centre with the support of conservative politicians.
At the event, Australian Conservatives Senator Cory Bernardi told "No" supporters they were under attack for being on "the right side of legal and moral history." Repeating a key point from the "No" camp, he suggested that a change to the Marriage Act could lead to the criminalization of thoughts or speech, according to the Australian Broadcasting Corporation.
"If the state redefines marriage it also redefines how you can speak, think, advocate, and believe about marriage."
The launch included the debut of an ad attacking "radical gender ideas," a reference to schools education programs that address concepts of gender identity and sexual orientation.
Polling shows that Australians have long been in favor of marriage equality. But multiple governments have maintained they wanted to keep the traditional definition in law. The latest Newspoll survey, released on August 22, said 63% of Australians were in favor of legalizing marriage between two men or two women.
Just 30% said they were opposed, with the rest undecided. Overall, about four-fifths of Australians are accepting of homosexuality in general, Pew Research data published in 2013 reveals
, one of the highest numbers in the world.
Voters have until November 7 to submit their forms.