At least one same-sex marriage opponent believes it will be highly unlikely additional religious protections will get the support of federal parliament.
Cabinet minister Peter Dutton wants further safeguards added to a private bill that will allow two people to marry but admits that will be "near impossible" given the numbers in the lower house.
"In this business, we face the reality of arithmetic and that is the reality in this parliament," he told MPs on Monday night.
Mr Dutton is against changing the Marriage Act but has committed to voting 'yes' out of respect of the result of the postal survey - an idea he put forward when Tony Abbott's compulsory plebiscite failed.
He will, however, support "sensible" amendments to be put forward by his Liberal colleagues, including conservatives Michael Sukkar and Andrew Hastie.
They are seeking wide-ranging changes, including exemptions for civil celebrants, small businesses and religious charities, and two definitions of marriage - one for men-women and another for two people.
Mr Dutton denied it was an attempt to frustrate the process and delay the bill's passage, but to improve the legislation.
"I do believe Australians would support those safeguards, that's why it is important for us to have another process ... because I think there is a debate to be had in this country around religious and parental protections," he said.
The immigration minister believes enshrining further protections will have greater success following an inquiry into religious freedoms early next year, to be led by Philip Ruddock.
Mr Dutton was one of the last few speakers to address parliament on day one of debate on the bill in the lower house on Monday.
Malcolm Turnbull, Bill Shorten, Mr Abbott and four co-drafters of Liberal senator Dean Smith's bill all confirmed they will be voting 'yes'.
More than 100 MPs were slated to speak on it this week, although that could change if a final vote is to be brought on by Thursday - the last scheduled day of sitting for the year.