The picture of the battered young man was tweeted on Wednesday afternoon by the two-time Labor Prime Minister with a message saying it was a graphic illustration of the trauma the controversial postal survey would cause.

“So many warnings to Turnbull about what the postal vote could unleash. Now my godson Sean has been punched for standing up for marriage equality,” the tweet read.

Sean is pictured in a selfie taken on a bus with a large cut between his eyebrows and blood smeared across his face.

The tweet has been retweeted almost 500 times.

A Facebook post of the Bulimba 4 Marriage Equality group said Sean was confronted by a man who called him a “faggot” and then told him, “I hate f***ing faggots.”

According to the Facebook post Sean told him, “That’s ok, I don’t like you,” which caused the man to say, “Did you just call me a homophobe?”

When Sean replied he did the man allegedly walked over to him and punched him so hard it knocked his head back violently. The post said there were others at the bus stop who ignored the incident.

“No one at the bus stop did anything!”

The disturbing incident comes as voting packs for the same-sex marriage postal survey begin to arrive in Australian mailboxes.

From Sydney to regional Victoria, people have begun posting images on social media with their ballot papers. Many have also been taking snaps of themselves filling the forms in and posting them back. Those voting yes have used the hashtag #PostYourYES.

Some 16 million voting packs are progressively being sent out across the country over the next few days.

People have until early November to return them but experience from other postal votes suggests between 80 and 90 per cent could be returned within three days.

“My postal vote arrived today, will be posted today,” said one social media user.

“My wife & I have received our postal survey ballots, voted Yes 4 #marriageequality & returned our ballots back into the post,” said Bruce Taggart on Twitter.

But one person who won’t be voting yes is rugby superstar Israel Folau. On Wednesday, the NSW Waratahs player posted on Twitter that while he had “love and respect” for all people, he “will not support gay marriage”.

A Pentecostal Christian, Folau followed his statement with a love heart emoji, which some followers questioned the use of.

“What are you basing your opposition on?” asked one. “I’m trying to understand how you can say you love and respect people, but hold that view?”

On Wednesday, Australian Catholic Lobby head Lyle Shelton said claims of bigotry were being used to slur no campaigners.

“Homophobia doesn’t exist much in Australia,” Mr Shelton said at the National Press Club. This is despite various deeply troubling posters and leaflets suggesting gay people are child molesters having emerged in recent weeks.

Campaigners for both the yes and no same-sex marriage cases have called for more civil and informed debate, with Parliament now having passed rules banning hate speech during the survey.

Advocates of both sides of the argument say they have faced abusive comments for holding their views and expect more to come.

To keep a lid on the worst forms of hate speech, Labor backed a government bill on Wednesday to put in place a set of rules — backed up by penalties of up to $25,200 — for the campaign, which will end on November 15 with the declaration of the postal survey result.

It will be an offence to vilify, intimidate or threaten to cause harm to a person on the basis of their sexual orientation, gender identity, intersex status or religious conviction during the survey.

Advertisements will need to be authorised and broadcasters must ensure opposing views go to air.

“We want this process to be fair and for Australians to get the opportunity to have their say in an appropriate environment,” cabinet minister Mathias Cormann said.

Labor deputy leader Tanya Plibersek agreed the survey was unnecessary but the protections were needed to put some rules around what was already an “awful debate”.