The High Court is working on a timetable to hear the Commonwealth's challenge to ACT same-sex marriage laws.
The High Court could hear a challenge to the ACT same-sex marriage laws before any weddings are held.
Chief Justice Robert French told a directions hearing on Friday he was working towards having the case heard when the full court sits from December 3 to 6.
Commonwealth solicitor-general Justin Gleeson SC told the court he understood the ACT's law was likely to formally come into effect on November 7, which meant the first marriages could happen from December 7.
However, marriage equality advocate Ivan Hinton, who proposed to his partner Chris on Tuesday, thought the ACT law might come into effect earlier than the lawyers expected, meaning marriages could in fact be held before the court hearing.
He raised the prospect of mass weddings, saying his lobby group Australian Marriage Equality had registered interest in getting married from 800 couples.
"If we're going to have a very, very big bunch of weddings ... we're going to need a lot of celebrants and we're going to need big facilities," he told reporters outside the High Court in Canberra.
Mr Gleeson told the court if same-sex couples were married in December and the court subsequently overturned the law, that would have complications for property rights, wills, common law and equity.
The Commonwealth argues the federal Marriage Act is the "sole and uniform law" throughout Australia regarding marriage.
"The essential purpose of the federal act is to establish a single and indivisible form of marriage," Mr Gleeson said.
Similarly, he said the Commonwealth would object if the ACT decided to legislate a "trial marriage act" where marriages had a five-year sunset clause to allow people to get out without divorce.
ACT solicitors are expected to reply that because the federal law defines marriage as between a man and a woman, there is space for the states and territories to legislate for marriage between same-sex couples.
The ACT has until November 1 to file its defence to the Commonwealth's challenge and a court date will most likely be set at the next directions hearing on November 4.