At least two conservative Senators say they will try to amend Dean Smith's bill to allow conscientious objections to gay marriage if the results of the nationwide postal survey return a 'yes' result on Wednesday, despite Prime Minister Malcolm Turnbull saying the idea would never get through parliament.
Government sources confirmed it was unlikely a rival bill put forward by Senator James Paterson would see the light of day in parliament, given Senator Smith had struck a deal with Labor, the Greens and enough crossbenchers to have his bill to legalise same-sex marriage, which enjoys cross-party support, debated all day on Thursday.
The Australia Bureau of Statistics will announce at 10am the result of the postal survey, in which nearly 80 per cent of the population, or 12.6 million Australians, took part.
If the result is yes, Western Australian Senator Dean Smith will introduce his bill on Thursday. It will change the definition of marriage under the Marriage Act from "a man and a woman" to "two people".
The Smith bill would allow religious celebrants to refuse marrying gay couples and allow religious organisations to refuse gay couples permission to wed in their buildings and function halls.
Senator Paterson's rival bill, which has the backing of Coalition conservatives, goes much further.
It would allow parents to pull their children out of class if they are being taught about relationships "not consistent with a relevant marriage belief".
It also seeks to protect charities who campaign for traditional marriage and would extend the right to refuse service to gay couples not just to religious organisations and clergy but to all religious believers on the grounds of "conscientious objection" and the right to religious expression. This means florists, photographers and bakers would all be allowed to refuse services to gay couples and not face anti-discrimination action.
Conservatives argue that, because it is not discriminatory to support marriage as existing between a man and a woman, it should not be discrimination to express that view.
"I think it would have virtually no prospect of getting through the Parliament," the prime minister said.
Senator Paterson's bill was the result of the Senate Select Committee on an exposure draft marriage bill on which he sat. Its report recommended that "the right to religious freedom should be positively protected".
The committee was chaired by the South Australian Liberal Senator David Fawcett, who told Fairfax Media it was the better piece of legislation compared to the Smith bill.
"In the event of a yes vote I'd prefer the Paterson bill, which more completely reflects evidence presented to the Senate Select Committee," he said.
"I'm disappointed that people are focussing on the three per cent of Senator Paterson's bill that deals with bakers and are ignoring the 97 per cent which focuses on protecting parents rights, charities and protecting the freedoms of belief, speech and association."
"These are the critical areas we need to protect," he said.
"If the Smith bill ends up being the one debated, I will be supporting amendments, whether they're mine or put forward by someone else, because religious freedoms belong to all Australians, not just clergy" he said.
Senator Fawcett was joined by the Tasmanian Liberal Senator Eric Abetz, who told Fairfax Media he would definitely move amendments to Senator Smith's bill if the result is 'yes'.
"While I'm still hopeful of a 'no' vote, if the 'yes' vote is successful it will be important to protect freedom of speech, parental rights, freedom of religion and freedom of conscientious objection," he said.
"If Senator Patterson's bill is not allowed to be debated then amendments should be moved to the legislation to ensure the same protections espoused in Senator Paterson's bill.
"Senator Paterson's bill goes a long, long way to addressing and alleviating a lot of those concerns and in the event of a 'yes' vote, I think his is a blueprint to try and bring as much of the community together in circumstances where this is a difficult issue."
Western Australian Senator Linda Reynolds is one of the government senators who signed Senator Smith's motion for his bill to be introduced on Thursday. She said she reserved her right to vote for further religious protections.
"I support Senator Smith's Bill, but I also reserve my position to support amendments that seek to further increase religious protections," she said.
Any amendments to provide greater protections for religious people will only likely be moved in the Senate because there same-sex marriage supporters would have the majority in the lower house following the disqualification of Barnaby Joyce, who did not support change.
But government sources said it was likely the issue would end up being debated in the Coalition party room when parliament is scheduled to sit for its final fortnight of the year from November 27.