Andrew Broad says a plebiscite is the only way to achieve marriage equality in this term of parliament, because it's what the coalition promised before the July election.

"My support for the government is conditional that we honour our election commitments," he told reporters in Canberra on Tuesday.

Mr Broad refused to reveal whether any others would follow him in withdrawing support, but noted there were many MPs who believe the coalition should honour its election commitments.

Liberal Andrew Laming said a win in the plebiscite would represent a "flying colours victory" for the vote in parliament, hitting back at critics who warn it would be non-binding.

He criticised Qantas CEO Alan Joyce for saying he'd rather wait for same-sex marriage through a parliamentary vote.

"Alan, with the greatest of respect, there's plenty of same-sex Australians not prepared to wait," he said.

Ahead of a Labor caucus meeting, cabinet minister Mathias Cormann urged Opposition Leader Bill Shorten to get out of the way and back the plebiscite.

"Why is he so scared of the Australian people?," he asked.

Labor's marriage equality spokeswoman Terri Butler said it was ridiculous the draft Marriage Act amendments were released by Attorney-General George Brandis at five minutes to midnight.

She warned the bill would create new forms of discrimination - a second price same-sex couples would have to pay for marriage equality.

Ms Butler said the best way to achieve change was through a parliamentary vote.

"We could have marriage equality in this country legalised before the cricket season even starts," she said.

"We won't have to sit around watching tests with ads from anti-marriage equality people in the ad breaks, we can just actually have weddings."

Labor senator Louise Pratt, who is a mother in a LGBTI family, is comfortable about waiting for a parliamentary vote.

New Labor MP and paediatrician Michael Freelander has significant healthcare concerns about the plebiscite, fearing it puts unreasonable stress on the LGBTI community.

He also criticised what he called false statements being made about the children of same-sex parents, saying they have no worse health problems than others he sees.

Greens marriage equality spokeswoman Janet Rice turned on Labor, echoing Prime Minister Malcolm Turnbull who has accused the opposition of playing politics with the issue.

"Labor should have put the plebiscite out of its misery months ago," she told reporters.

"They have been playing politics, they have held onto it and even this morning they're saying there's still potentially negotiations going on over removing the public funding for the plebiscite."

Treasurer Scott Morrison said it was disappointing the opposition wanted to deny Australians a right to have a say on the issue.

"Labor are being I think very, very bloody-minded about this," he told Ray Hadley on 2GB radio.

Liberal MP Melissa Price suggested the government's bill - to be put to the party room on Tuesday morning - would be open to tweaking.

"Like we have done with superannuation, like we have done with the backpacker tax I'm quite confident that we'll get to a position where the party is happy with what we have," she said.