Civil celebrant associations say they don't want the right to discriminate against same-sex couples, despite Attorney-General George Brandis' bid to let their members refuse gay weddings.
The Australian Human Rights Commission also dismissed the chief law officer's call on Tuesday, arguing it would wind back Australia's existing anti-discrimination laws.
But the commission endorsed Immigration Minister Peter Dutton's idea to re-examine and potentially expand religious freedom provisions more generally in the new year.
Senator Brandis argues civil celebrants should be able to refuse to officiate ceremonies on conscientious grounds, just as religious ministers are allowed to refuse weddings on religious grounds.
But representatives of Australia's 8500 civil celebrants said they had not asked for such an exemption, and were comfortable with Liberal senator Dean Smith's bill as it currently stands.
The bill already provides a three-month "transfer" period for existing celebrants register as religious celebrants if they wish to be entitled to decline to perform same-sex weddings.
"We don't approve of exemptions," said Dorothy Harrison, chair of the Coalition of Celebrant Associations. "We feel that if that's the law of the country, then that's what you do. We have discrimination laws and we have to live by them."
She was backed by Rona Goold, founder of the Civil Celebrations Network, who said further exemptions would open up a slippery slope for celebrants to turn couples away.
"Who are going to be the ones who are actually required to uphold the law?" she asked. "Don't bring in a law to get rid of discrimination and build in more discrimination."
The AHRC, which has quietened its public advocacy under new president Rosalind Croucher, also took Senator Brandis to task over the proposal. Human Rights Commissioner Ed Santow said the organisation would have "strong concerns" about any proposal to exempt civil celebrants.
"The price of marriage equality can't be that we wind back our anti-discrimination laws," he told Fairfax Media. "If you're a civil celebrant performing civil marriages, the ordinary anti-discrimination law should apply."
However, Mr Santow agreed with Mr Dutton and others that a debate about a religious freedom charter would be "very appropriate" if undertaken separately to the marriage equality law.
He has previously lamented the "real gaps in how Australian law protects freedom of religion" and urged freedom of religion to be written into anti-discrimination laws.
Senator Brandis is one of the government's strongest proponents of same-sex marriage and has rejected calls for goods and services providers to be allowed to discriminate against same-sex couples. But on Monday's episode of Q&A he argued civil celebrants were in a different category.
"I don't regard them as merely public servants," Senator Brandis said. "They're officiants of the ceremony, and if they have a conscientious objection to a particular form of the ceremony, I think it's quite wrong to force them to officiate in a way that would violate their conscience."
A survey of 1500 civil celebrants conducted by the Coalition of Celebrant Associations found just 3 per cent would resign if compelled to perform same-sex weddings. Eighty per cent said they would happily marry same-sex couples, while 10.5 per cent said they would consider refusing "discreetly" (i.e by claiming to be unavailable).
Official statistics show 75 per cent of Australia's 110,000 annual weddings are now performed by civil celebrants, despite religious celebrants outnumbering their civil counterparts almost three to one.
Senator Smith's bill will be debated in the Senate next week and then in the House of Representatives. It is expected to become law by Christmas after the resounding "yes" vote in the postal survey.
with Tara Hayes
