Turnbull government ministers have largely rejected a push by Coalition conservatives to overturn sections of anti-discrimination law in the event same-sex marriage is legalised.
Liberal MP James Paterson on Monday released a bill that would permit same-sex marriage but allow a wide range of service providers to discriminate against gay couples planning a wedding.
The exemptions would extend to any person or business refusing to co-operate with the staging of a same-sex wedding on religious or "conscientious" grounds, protecting them from civil litigation.
It would override existing state and territory anti-discrimination laws, stating plainly that when the two come into conflict, the federal law would prevail.
Senator Paterson's bill also establishes what he calls a "relevant belief" about homosexuality itself, protecting anyone who expresses a belief that same-sex relationships are unholy or immoral, or that "the normative state of gender is binary".
The Victorian senator is a "yes" voter but a longstanding advocate for individual liberty. His bill, developed in consultation with Coalition conservatives, allows for significantly more discrimination than the one already produced by West Australian Liberal senator Dean Smith.
Prime Minister Malcolm Turnbull and his cabinet ministers backed Senator Smith's bill on Monday, although they suggested it would be amended in line with the will of the Parliament.
Mr Turnbull said Senator Smith's bill "has been around for some months and is clearly a good bill to start with". He was joined by Finance Minister Mathias Cormann, a conservative "no" voter, who said the Smith bill was "a good starting position" though could be improved.
Crucially, both men - as well as the manager of government business, Christopher Pyne - indicated it would be the Senate that decides the fate of both bills, not the Coalition party room. Labor has already signalled its support for Senator Smith's proposal, giving it a clear advantage.
The results of the same-sex marriage postal survey will not be released until Wednesday, but the publication of Senator Paterson's bill is seen as an attempt by conservatives to shape the debate in the likely advent of a "yes" vote.
The bill was rubbished by the Equality Campaign, whose director Tiernan Brady called it "a rebuke to the Australian people".
"It literally is the opposite of what the people will have voted for," he said. "We're not going back to a time when we have signs on windows saying certain people can't apply or certain people won't be served. That is precisely what the bill does."
Law Council of Australia president Fiona McLeod said the winding back of anti-discrimination laws was "extraordinary and perilous", and without precedent in Australia.
The Paterson proposal also tells religious and civil celebrants it is within their power to decide if a person is "a man or a woman", and allows them to ignore the legal status of an intersex or transgender person if they believe the person isn't really male or female.
In a key bone for conservatives, the bill would not actually remove the definition of marriage as between "a man and a woman", inserted under John Howard's leadership in 2004. Instead, it would add a second clause declaring marriage can also be "the union of two people".
And the bill would allow parents to withdraw their children from school classes that don't accord with their own understanding of marriage.
Senator Paterson told Fairfax Media his proposed exemptions would only extend to providers of goods and service "directly connected" with a same-sex wedding, such as venue hire, audio-visual equipment, cakes and flowers.
It would not include gifts bought by wedding guests or the taxi fare to attend a ceremony or reception.
"It's not about the person, it's about the event. You cannot decline to supply a person based on their own characteristics [but] you can decline to participate in their wedding," Senator Paterson said.
"Thirty to 40 per cent of Australians will vote 'no' and I don't want to see their rights and freedoms diminished at all."