Mr Beazley says he does not support the federal government's move to scuttle the ACT's homosexual union laws.
Prime Minister John Howard today said the ACT's laws challenge the Commonwealth's Marriage Act.
But Mr Beazley said that was not the case.
"I regard the Marriage Act as sacrosanct, I regard marriage as an institution between a man and a woman," Mr Beazley said.
"The ACT's legislation does not offend against the commonwealth Marriage ACT," he said.
"The (ACT) chief minister and his colleagues were very careful to make sure it didn't.
"It's a matter of discrimination and I am against discrimination. That is what the ACT is talking about.
"I do not support the commonwealth doing this to the ACT government.
"I will certainly argue that view within caucus."
Mr Beazley said the Commonwealth should only contemplate intervening in state and territory law when lives are at risk.
With the Howard government arguably framing same-sex unions as a wedge issue, making the Labor response come in the form of a nod to States' rights is probably a wise way to play it. But stop waffling, Kim. Make your message clear.
Stronger language, please. Tell 'em to get a bloody brindled dog up 'em.