The Abbott coalition will seek legal advice on the ACT government's same-sex marriage bill in a clear sign they'll consider repealing it if they deem it outside the law.
The ACT government on Thursday introduced a Marriage Equality Bill to legalise same sex marriage that will allow gay and lesbian couples to be married in the territory by the end of the year.
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It's expected to pass the Legislative Assembly as soon as October, with the Greens supporting the Labor minority government on the move.
That would make the ACT the first Australian jurisdiction to allow same sex marriage.
However, when asked about the legislation, Liberal Prime Minister Tony Abbott replied the ACT government was entitled to do what it wanted - as long as it stayed within the confines of the law.
"(Attorney-General George Brandis) will be seeking legal advice on precisely how far the ACT can go on this," he said.
"As you know under the constitution the Commonwealth has responsibility for marriage and the attorney will be seeking advice on precisely how far that extends."
Chief Minister Katy Gallagher earlier said her government was working towards people being able to marry under the law before the end of the year.
But she conceded it could be subject to challenge in the High Court or overturning by a vote of both houses of federal parliament.
"We know there's some risks attached with this legislation," Ms Gallagher told ABC radio.
"But we don't think those risks should stop us proceeding with a commitment we made to the people of the ACT in the election campaign last year."
Under the law, anyone who can't marry under the Commonwealth's Marriage Act will be able to wed.
The commonwealth act defines marriage as a union between a man and a woman.
Couples from outside the ACT would be able to get married in the territory but their relationships may not be recognised in their home state.