Religious believers would be vulnerable to discrimination suits and some could lose their jobs, promotions, businesses and political careers if same-sex marriage is legalised, the Catholic Archbishop of Sydney says.
Anthony Fisher supported the 'no' vote in the same-sex marriage postal survey during his homily at mass on Sunday, telling worshippers the government should "keep out of the friendship business and out of the bedroom".
"The state has no business telling us who we should love and how, sexually or otherwise," he told the St Mary's Cathedral congregation.
"The only kind of friendship the state has a proper interest in recognising and regulating is heterosexual marriage, because that's what leads to children - new citizens - and gives them the best start in life."
Archbishop Fisher said it was best for children to have a mother and a father, and that's what marriage was about.
He said the vote had implications for religious freedom and it wasn't unreasonable for people to say they couldn't support a change to marriage laws until protections were in place.
"If overseas experience is anything to go by, if marriage is redefined it will be very hard to speak up for real marriage anymore - in schools, at work, socially," he said.
"Traditional believers will be vulnerable to discrimination suits and other kinds of bullying for their beliefs. Some may lose their jobs, promotions, businesses, political careers."
Archbishop Fisher previously weighed into the marriage debate last month when he and Dan White, the executive director of Sydney Catholic Schools, sent parents a letter encouraging them to vote 'no' in the postal survey.
The result of the voluntary postal survey will be announced on November 15.