Former PM Tony Abbott says he'll respect the outcome of a postal vote on same-sex marriage.
Malcolm Turnbull has ruled out further action on same-sex marriage if the High Court strikes down the government's national postal ballot.
The Australian Bureau of Statistics has begun work on the $122 million voluntary poll, with forms due to be posted by September 12 and completed by November 7 with a result to be announced on November 15.
A private member's bill would then go to parliament by the end of the year.
Marriage equality activists on Thursday launched two High Court bids to head off the ballot, saying it breaches the constitution and funding the vote without legislation exceeds the government's power.
The challenges involve the Human Rights Law Centre and Public Interest Advocacy Centre.
When asked what would happen if the court struck down the ballot, Mr Turnbull said: "Our policy is very clear. We will not facilitate the introduction of a private member's bill on this matter unless the Australian people have given their support through a 'yes' vote through this national vote."
Labor leader Bill Shorten quashed suggestions the party would boycott the poll, telling parliament he would campaign for the "yes" case.
It was a waste of taxpayers' money and he would not blame voters for chucking their ballot paper in the bin but they should not sit on the sidelines.
"The most powerful act of resistance is to vote yes for equality," Mr Shorten said.
"Voting yes is not about endorsing this process, it is about refusing to walk past our fellow Australians when they need us."
Labor has raised questions about missing legal protections against bribery and intimidation, the short time frame for updating the electoral roll, the ability of voters in remote areas to return their ballot papers, the lack of authorisation of campaign material and the inability to challenge the result in the Court of Disputed Returns.
Mr Turnbull said if Labor wanted the Electoral Act and all its protections to apply, it should have supported the compulsory plebiscite in parliament.
Former High Court judge Michael Kirby wants the plan abandoned, saying he is instead happy to wait to wed his partner of 50 years.
"I feel as a citizen I'm being treated in a second-class way," he said of the ballot.
Nationals MP Andrew Broad, who has threatened to quit the government if the coalition changes its plebiscite policy, is pleased Australians can have their say.
Asked about a possible boycott, the MP said: "There were people who chose not to vote for Donald Trump because they walked away from it and they got Donald Trump, didn't they?"
Treasurer Scott Morrison defended the $122 million price tag of the postal ballot, insisting "keeping promises is money well spent".
The minister in charge of the ABS Michael McCormack fended off criticism of the agency, which has come under fire over its handling of the census, saying it would do its best to ensure the officially titled Australian Marriage Law Postal Survey is conducted properly.