The Court's second day of hearings focused on the government's case that the survey is constitutional and its cost justified.
Marriage equality advocates want to stop the government's upcoming postal survey because its funding hasn't been approved by parliament.
The $122 million needed is to be sourced from a fund used for "urgent and unforeseen circumstances".
Solicitor General Stephen Donoghue told a sitting of the High Court in Melbourne the federal Finance Minister has the power to do so.
He argues the survey would be "unforeseen" because the money wasn't in the last Budget, and "urgent" because the government cannot wait for the next Budget.
He says government policy can be considered "urgent" business, given such funding has been previously allocated to sports stadiums and arts centres.
Mr Donaghue also responded to claims put before the Court that the survey allows the public to vote on the validity of same-sex relationships.
He says any aspersions on same-sex marriage derive from the Marriage Act as it stands, and from any third parties engaged in an anti-same-sex marriage campaign - NOT from the postal survey.
Mr Donaghue also argued in favour of the Bureau of Statistics running the survey, saying it is a statistical exercise and certainly not a vote.
Tiernan Brady is the executive director of the Equality Campaign.
He's told the National Press Club in Canberra if the High Court ultimately decides to scrap the survey, it would not damage the argument in favour of marriage equality.
"If the court case is successful, that momentum, that energy is going to refocus on the next place where the decision needs to be made anyway, which is parliament, with this clear message: get it done."
But if the postal survey does go ahead, Australian Marriage Equality co-chair Janine Middleton is urging everyone to take it seriously.
"This isn't a referendum on whether we should have a republic, (where if) we lose, you come back in 20 years' time. This is... the LGBTI people of this country are going to keep fighting and campaigning until they have the respect and dignity they deserve."
The High Court will announce tomorrow afternoon whether the ABS should proceed with the survey, just five days before it's due to starting sending out postal forms.
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