Australia's High Court has ruled the Federal Government's $122 million same-sex marriage postal survey will go ahead.
The Federal Government has welcomed the High Court ruling, saying the survey would continue as planned and the final result would be declared by the chief statistician at 11.30am on 15 November.
Prime Minister Malcolm Turnbull urged all eligible Australians to vote in the survey.
"This is a great example where every Australian can have a say and we can, as a Commonwealth of Australia, embrace this important social change, consider it and make a decision," Mr Turnbull told Parliament after the decision was handed down.
Opposition Leader Bill Shorten again invited Mr Turnbull to sign a joint letter with him recommending a vote for "marriage equality".
Mr Turnbull indicated he was sceptical co-signing a letter, "would increase the case for the Yes vote".
"The Leader of the Opposition can make his case and I will make mine," the Prime Minister said.
The Greens said they were disappointed with the result in the High Court but declared they would now campaign hard for a Yes vote.
The Australian Bureau of Statistics will start sending out ballot papers from Tuesday .
The paper will ask: "Should the law be changed to allow same-sex couples to marry?"
Returning the survey and participating in the ballot is optional.
Forms must be returned by 6pm on 7 November at the latest.
If the result is no, the Prime Minister has said the government would not support a private members' bill on the issue going ahead in Parliament.
But if those who participate in the survey vote yes, then Mr Turnbull has said a private members' bill could be debated and voted on by the end of the year.
The government has also said it would move to legislate to ensure advertising for the Yes and No cases met the usual electoral rules, including protections against malicious publications and bribery.
The High Court's ruling means the advertising for both sides will intensify.
There will also be pressure on federal parliamentarians to explain what they will do if Australians vote yes.
So far, some MPs have pledged to "respect" the result of the survey but have not said whether that meant they would vote according to the overall national result or instead back the result from their electorate or state.