Pauline Hanson says she believes polygamy and underage marriage could be among the unintended consequences of legalising same-sex marriage.
Despite raising concerns, the One Nation leader said she is still unsure whether she will support the bill on same-sex marriage before the Senate and will give her party colleagues a free vote on the issue.
"My concern is that, in time to come, the Parliament and its members could at any time change this [definition] to include multiple marriages or marriages of people under a certain age," Hanson told Parliament yesterday.
Hanson will move an amendment to the bill to protect civil celebrants who want the right to refuse to marry gay couples.
"I don't believe we are fully aware of the ramifications this is going to have on our society," she said.