Liberal senator James Paterson has proposed an alternative same-sex marriage bill.
But they have been roundly rejected by other ministers, including the country's chief law officer, Attorney-General George Brandis.
Senator Smith said he was hopeful the Yes vote would prevail, but even if Australians voted No he would still introduce the Bill to the Senate this week.
Fellow Liberal Dean Smith also has a private bill ready for parliament.
"If you're a gay man or gay woman and you go into a florist and say, "I'd like to buy a bunch of flowers", it's just wrong and illegal for the florist to say, "I don't serve gay people" - just as it would be wrong or illegal for the florist to say to an Indigenous person, "I don't serve Indigenous people".
The Senator from Victoria said his bill would allow any Australian to declare that they would not participate in a same-sex wedding if it violated their religious beliefs.
But Mr Turnbull on Tuesday warned Australians would not welcome moves to wind back anti-discrimination protections.
The Paterson bill ensures exemptions for ministers of religion and celebrants with genuine belief and allows a limited form of conscientious objection, and also seeks to protect freedom of speech and guarantee the right of parents to opt their children out of school classes that conflicted with their values.
SYDNEY == The head of Australia's marriage equality push has slammed calls for anti-discrimination exemptions to be legalised under the guise of "religious freedoms" in the event of a yes vote in the postal survey, claiming such moves would be against the spirit of the support for the reform.
The national director of Liberals and Nationals for Yes, Andrew Bragg, has said a marriage bill should be guided by three principles: "Firstly, existing discrimination in the Marriage Act should be eliminated; secondly, a strong protection for religious freedom should be provided; and thirdly, we should not reintroduce commercial discrimination in Australia". "That's the reason we have the parliamentary debate".
Senator Smith last night exclusively told The Sunday Times his Marriage Amendment (Definitions and Religious Freedoms) Bill 2017 would be tabled in Parliament the next day.
The survey result will announced on Wednesday. "This Bill will encroach on many of these protections in an extraordinary and perilous way", she said in a statement.
"There will no doubt be plenty of amendments and.at the end of it they will come to a conclusion on an amended bill".
The results of the same-sex marriage postal survey land tomorrow, and we'll know at 10am on the dot how the people of Australia have voted.