The High Court has upheld the Federal Government's postal survey on same-sex marriage, ruling the $122 million voluntary ballot can go ahead.
In a blow to marriage equality campaigners who challenged the Government's right to run the survey, the full bench of the court dismissed their case on Thursday and ruled the postal vote could proceed.
The survey is being run by the Australian Bureau of Statistics and survey questions are expected to be mailed to households across the country from early next week.
MP Andrew Wilkie said outside the court the government will be in strife if there is a strong turn-out for the 'yes' campaign and the coalition delays delays a vote on same sex marriage.
"We are one of the few developed countries in the world without same sex marriage," Wilkie said.
"This is stone age stuff, the situation in this country at the moment.
"We need the overwhelming majority to be returned and we need a strong yes vote."
Same Sex Marriage Campaigner Alex Greenwich said the decision marked the start of the yes campaign.
The yes campaign begins today.Alex Greenwich
"It begins today at train stations right across the country, as you will see here, just around the corner at the end of this press conference," Greenwich said.
"It begins with a national television campaign, encouraging people to get out the vote."
Prime Minister Malcolm Turnbull said he wanted every Australian to have their say in the survey as news broke about the High Court's ruling.
"We encourage every Australian to vote in this survey, to have their say, and as I have said in this House and in many other places, Lucy and I will be voting yes and I will be encouraging others to vote yes," he told parliament.
Prior to the ruling, Labor Leader Bill Shorten said the Opposition would continue campaigning for a "yes" vote.
"We will campaign most energetically, most passionately, for people to vote Yes in the survey," he told reporters in Canberra.
"And then we would expect that upon the successful Yes vote in the survey, that the Parliament immediately brings a Bill to the Parliament to vote on, and a full, free vote."
The Greens also expressed their dismay at the ruling.
"It is shameful that the government has chosen to put a matter of human rights to a public opinion poll," said Senator Janet Rice.
Executive Director of The Equality Campaign, Tiernan Brady, called for respect in the campaign for same-sex marriage.
"We haven't a moment to lose and we are hitting the ground running with hundreds of thousands of supporters talking about why marriage equality matters," Brady said in a statement.
"This is a vote about the worth, dignity and status of members of our family, friends, workmates and neighbours, and across the country people are standing up for them.
GetUp! Marriage Equality Director Sally Rugg said the government had "another thing coming" if it thinks same-sex marriage campaigners are not prepared to win.
"Our secret weapon is one-on-one conversations between ordinary Australians – connecting with voters and making sure the huge momentum for marriage equality translates into Yes votes," she said in a statement.
"We'll use this opportunity to build a better country – for young LGBTIQ people, for our neighbours, our family, and for an Australia that celebrates diversity, cherishes love and strives for equality."