The bill to legalise same-sex marriage is all-but-certain to pass the Senate unchanged on Wednesday after a series of amendments from Coalition senators were voted down.
While the Dean Smith bill already allows priests and other religious celebrants to refuse to wed same-sex couples on the basis of their faith, a number of senators wanted the protection extended to civil celebrants with a "conscientious objection".
But the amendments from Senator James Paterson, Senator George Brandis and Senator Matt Canavan were voted down last night after a debate that stretched until just after 11pm.
The civil celebrants exemption from Senator Brandis was defeated 25 - 38, while another amendment that would have extended a "right of any person" to "manifest his of her religion" was defeated 27 - 36.
While the Senate will still need to vote on some amendments from One Nation, the Greens and David Leyonhjelm, the bill is likely to proceed to the Lower House without any changes.
Already, one Nationals MP has blasted Prime Minister Malcolm Turnbull for failing to protect religious protections.
"Look, I think, in my view, there's been a complete lack of leadership," MP Andrew Broad told ABC Radio.
Mr Broad said the government should have tried to build more religious exemptions into the bill from the beginning, rather than allowing the amendments to fail on the floor of the Senate.
But Coalition frontbencher Senator Simon Birmingham, who voted against the changes, said Malcolm Turnbull had shown "very strong leadership" by enabling the bill despite some of his colleagues trying to "derail the process".
Senator Birmingham said while his Coalition colleagues in the House of Representatives have the right to raise more amendments, the Smith bill now "ought to pass the [Lower] House in its current form".
Labor voted as a bloc to defeat the changes to the original Dean Smith bill - which was developed in a cross-party committee- with the support of the Greens, the Nick Xenophon Team and independent senator Derryn Hinch.
"To proceed with this amendment would undermine the important principle that civil celebrants, as secular representatives of the state, should be bound by antidiscrimination legislation," Labor's Louise Pratt told the Senate in a closing argument.
Attorney-General George Brandis said he was confident the bill would pass the Senate on Wednesday before proceeding to the Lower House.
The remaining amendments from One Nation and Senator Leyonhjelm are both aimed at protecting civil celebrants, similar to the changes already rejected.
The Greens amendments, set to be opposed by Labor, would make it harder for civil celebrants to refuse to marry same-sex couples.
On Tuesday, the Senate also blocked a move to create two definitions of marriage - one between a man and a woman and the other as between two people.
That was included in one of five amendments proposed by conservative Liberal senators James Paterson and David Fawcett, which were comfortably defeated.
