The federal government is considering whether it should block the ACT's proposed same-sex marriage legislation.

The ACT government introduced a bill to permit same-sex marriages into the Legislative Assembly on Thursday morning. It is expected to pass the 17-member Assembly with the support of all eight Labor and the only Greens member.

Mr Abbott later said the Commonwealth had constitutional responsibility for marriage and Attorney-General George Brandis would seek advice on the ACT bill.

"The ACT is entitled to do what it can within the law," Mr Abbott said.