The opposition leader is championing his bill to legalise same sex marriage, while the Greens say its legislation has a better chance of cross-party support.
It comes as the government tries to head off a potential internal split over who pays for the 'yes' and 'no' cases in a gay marriage plebiscite.
The opposition benches in the lower house were full as Labor leader Bill Shorten introduced legislation to legalise same sex marriage.
"Today we can bring a new measure of hope and happiness to the lives of tens of thousands of Australians whose love has been denied equality under the law for too long. Together, we can vote to make marriage equality a reality."
In introducing the legislation, Bill Shorten and the Labor party demonstrate their official opposition to a non-binding plebiscite on the issue.
The plebiscite is the Coalition's preferred method of putting the question to Australians.
The public vote comes with a price tag of up to $160 million, and doesn't bind members of parliament to abide by the result.
Being so similar to a referendum, the question politicians now face is whether taxpayers' money should be directed to funding a 'yes' and 'no' case in a plebiscite.
Former Abbott government minister Kevin Andrews says it should.
"If there's a plebiscite, there ought to be the opportunity for both cases to be put fairly to the Australian people and for them to make up their minds on that basis. That's how we run referenda. This is a time-honoured way in which we have conducted these public discussions in Australia for over a century now."
The Liberal backbench is grappling with the issue.
Western Australian Liberal Senator Chris Back says there's a precedent for equal funding.
But he says that doesn't necessarily mean money needs to spent by a government trying to control its spending.
"This whole issue has been so well canvassed that I doubt there needs to be much funding for either side because the issues are well-known, they are well-prosecuted."
But Bill Shorten says only one side of the debate would need public funding.
"A 'no' campaign would be an emotional torment for gay teenagers. If one child commits suicide over the plebiscite, than that is one too many."
Former prime minister Tony Abbott says the recent election campaign shows Australians can have civilised debates.
"If we are capable of debating who should run the country we're more than capable of having a similar quality of debate about whether we want to preserve marriage, as it's always been, or whether we want to change it."
Mr Abbott's reference to marriage "as it's always been" is not quite accurate.
The Howard government changed the Marriage Act in 2004 - without a plebiscite - to specifically refer to marriage being "the union of a man and a woman".
But there's more to this headache for the Coalition.
Labor's attempt to legalise same-sex marriage by a vote in Parliament was immediately followed by a separate attempt from the Greens' Adam Bandt and minor parties.
"If we all work together, wedding bells can be sounding before Christmas this year and at the end of the day what matters is that marriage equality is passed. The leader of the opposition is right, ultimately no-one will care whose name appeared on what position on the bill."
With both the competing bills tabled in Parliament, they have moved into the second reading stage.
They'll be debated over the next few sitting periods before the lower house votes on whether to take the bills any further.
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