The Senate will consider a cross-party same-sex marriage bill all this week, which marriage equality advocates expect to deliver a decisive win for the reform being legislated by Christmas.

Although Coalition conservatives have signalled a willingness to fight for amendments to the cross-party bill, Labor and marriage equality advocates believe few, if any, stand a chance of winning Senate support.

The Turnbull government cancelled the lower house’s sitting this week and disclosure of senators’ foreign citizenship and steps to renounce it are not due until Friday so political debate in Canberra will centre on marriage although political fallout from the Queensland election will continue.

The cross-party bill, authored by the Liberal senator Dean Smith, has support from Labor, the Greens, the Nick Xenophon Team, Derryn Hinch and is also co-signed by the Liberal senators Linda Reynolds and Jane Hume, which advocates believe indicates there is little appetite even within the Coalition for major changes.

Labor estimates that more than 45 senators support marriage equality and others have promised to vote yes or abstain after the postal survey returned a 61.6% vote in favour of same-sex marriage.

In earlier Senate debate on the bill, the leader of the Australian Conservatives, Cory Bernardi, conceded that “this bill is going to pass” and although he would push to protect “religious freedom and freedom of speech”, he acknowledged “the numbers are against us”.

“You guys have the numbers to do whatever you want with this bill– to go forward,” he said. “I would only ask that you consider some of our concerns.”

Senator David Leyonhjelm has tabled amendments to allow civil celebrants and private service providers to refuse same-sex weddings but conservatives including Liberal David Fawcett have conceded they do not have the numbers to reintroduce commercial discrimination.

The prime minister, Malcolm Turnbull, has attempted to head off calls for amendments first by publicly arguing the bill does not harm religious freedom then by establishing an inquiry to separately consider the issue, reporting next year.

The attorney general, George Brandis, has said he will move a new amendment to allow civil celebrants to reject same-sex weddings and suggested adding a “declaratory statement” that nothing in the bill harms religious freedom in article 18 of the International Covenant on Civil and Political Rights.

Marriage equality advocates believe that only that declaratory amendment and the possible extension of the category of religious marriage celebrants to new celebrants stand a chance of success.

Labor has rejected demands for amendments, which could only succeed if they drew support from Coalition supporters of same-sex marriage, the crossbench including One Nation and half a dozen Labor members who have reserved their position.

Nevertheless conservatives will also argue for parental rights to withdraw their children from classes that clash with their marriage views and to shield charities from possible loss of funding or charitable status.

On Monday conservative Coalition ministers Angus Taylor, Zed Seselja and Michael Sukkar complained that moderates had betrayed them by backing the cross-party bill, the Australian reported.

Speaking to ABC’s AM, the Liberal MP and supporter of same-sex marriage Warren Entsch said the trio had “the responsibility to talk within their portfolios” and could raise objections in the partyroom or parliament.

“What I’m saying to these guys – these ministers – by all means, if you want to go chasing religious exemptions, please do so, but do us a favour and step down from your portfolios, you can do so then without breaching ministerial codes,” he said.

Smith said opponents of marriage equality had “failed to substantiate their claims with clear evidence [that] existing religious freedoms in Australia’s various laws are insufficient”.

On Sunday the Sunday Mail published a letter from the tax commissioner, Chris Jordan, to Smith that concluded that amending the Marriage Act would not have an effect on tax deductible status.



“Similarly, lawful refusal to conduct a marriage ceremony – in accordance with the future Marriage Act – will be unlikely to effect [deductible gift recipient] endorsement,” he said.



The Equality Campaign’s executive director, Tiernan Brady, told Guardian Australia the people had told parliament to “do your job, it’s time to pass marriage equality”.

“We went to the bother of spending $100m asking if LGBTI Australians should be treated the same under the law of the land and the Australian people said incredibly clearly yes.”

He said there was nothing to stop the prime minister’s stated ambition of legislating marriage equality by Christmas from being achieved.