Conservative Liberal MP Kevin Andrews has been criticised by the Greens for apparently comparing same-sex relationships to his friendships with his cycling mates.
Mr Andrews, a longstanding opponent of same-sex marriage, on Monday warned of the "boundaries" around the definition of marriage being stretched.
"There are all sorts of affectionate relationships," he told Sky News.
"I have an affectionate relation with my cycling mates who we go cycling on the weekends - but that's not marriage. Why doesn't the law have a place in those sorts of relationships."
Mr Andrews explained that those relationships didn't have a place in law because "historically, across cultures and civilisations" marriage was about "the protection of the vulnerable".
The former Liberal frontbencher denied he was suggesting same-sex relationships did not have the same depth.
"That's fine, and I have commitments with friends, I have affectionate relationships with friends as well.
"I hope he's his friend, as well as his partner, if you understand what I'm saying.
"The question is where do you draw the boundary around what we understand as marriage, what influence does this then have on the rest of society and what are the consequences of this."
Mr Andrews also cautioned about how "any set of arrangements can be put in place" if the definition of marriage changed, while denying he was suggesting polygamy.
"Because after all it's only, I suppose a belief and emotion about a particular arrangement that applies then what's traditionally been the case," he said.
"Once you change the boundary, the question is where do you, with any sort of logic, draw that boundary.
"In a world in which what has been advocated increasingly through things like the safe school program about their being neutrality and fluidity in relation to the way in which people identify with different genders, this is a pathway which will lead to anybody claiming whatever agenda they like as just two people being able to being legally be married in a relationship."
"People can make arguments around marriage equality that I think are respectful. But what he needs to understand is we're talking about two people who love each other and the law says if you're two people who love each other you happen to be a man and a woman we'll sanction that but we're not going to sanction any other form of relationship."