Australia's highest court has cleared the way for the government to conduct a public survey on whether gay marriage should be legalised.
Gay rights advocates had argued in the High Court that the government did not have the power to conduct the 122 million Australian dollar (£75 million) postal survey without Senate approval, but the court dismissed that challenge.
Opinion polls show most Australians want same-sex marriage legalised, but many advocates question how representative of attitudes the postal survey would be.
They want Parliament to decide the issue without consultation with the public.
The government has already begun printing the ballot papers, which are to be mailed to more than 16 million voters nationwide starting on Tuesday.
Results will be announced on November 15, but legislators are not bound to accept the outcome.
Prime minister Malcolm Turnbull welcomed the court ruling and urged all Australians to take part in the survey.
He told Parliament that he and his wife "will be voting yes and I will be encouraging others to vote yes, but ... above all, I encourage every Australian to have their say because ... I respect every Australian's view on this matter".
Many opponents of gay marriage support the survey, although some conservative legislators have said they will not vote for a change in the law even if a majority of Australians want reform.
The postal survey was the second choice of Mr Turnbull's conservative government, which had promised a rare, compulsory vote known as a plebiscite, but the Senate refused to approve 170 million dollars (£104 million) for such a vote.
Market researchers have said that telephone opinion polling could more accurately gauge the public's view in each of Australia's 150 electoral districts for around a million dollars (£610,000) - a fraction of the postal survey's cost.