Bill Shorten has blasted a "disgusting" poster carrying the slogan "stop the fags" which has been seen in a Melbourne laneway in the lead-up to a postal survey on same-sex marriage.
The poster, which depicts a child cowering below two people brandishing rainbow belts, lists statistics from a widely discredited study on children raised by same-sex couples.
It appears to trace back to the message board of a neo-Nazi website.
"Labor opposed this postal survey because we feared exactly this kind of hurtful filth would emerge," Mr Shorten posted on Facebook.
"This kind of garbage isn't 'debate', it's abuse. I'm so sorry that LGBTI Australians have to put up with it. Let's make sure there's an overwhelming 'Yes' vote in response."
A 2016 study by Reverend Paul Sullins from the Catholic University of America claims children raised by gay parents are at higher risk of abuse, depression and obesity.
But gay rights activist Rodney Croome said the Australian Institute for Family Studies found children raised by same-sex couples had the same outcomes as other children, contradicting claims made in the poster.
"Overall, research evidence indicates that children raised in same-sex parented families do as well emotionally, socially and educationally as other children," he said.
Meanwhile, Mr Shorten has urged opponents of marriage equality not to throw other issues into the mix in the lead-up to a postal survey.
"If we have got to have this vote, don't muddy the waters, don't cloud the issues by trying to throw every issue in including the kitchen sink," he told reporters in Sydney.
Attorney-General George Brandis has declared he won't be "tricked" by Tony Abbott and others trying to broaden the marriage debate into one about religious freedom.
Mr Abbott doubled down in response to Senator Brandis.
"The best way of standing up for traditional values, the best way of saying that you don't like the direction our country is headed in right now, is to get that ballot paper out and vote no," he told 2GB radio on Monday.
The former prime minister warned of potential consequences for religious educators, adoption agencies and school programs if same-sex marriage was legalised.
"If we have officially sanctioned de-gendering marriage, it's very hard not to see de-gendering come in in so many other areas as well," he said.
"It isn't just about marriage. Sure, marriage is the immediate focus, but there are lots and lots of implications here, and we've got to think them through before we take this big leap into what I think is the dark."
