OF ALL the reasons to say "no" to gay marriage this has to be the most bizarre.

Former cabinet minister Kevin Andrews has said same sex relationships were simply "affectionate relationships", the kind he might have with the members of his cycling group.

In contrast, marriage was a completely different institution that should remain between a man and a woman.

Mr Andrews spoke as the country gears up for a postal survey on same-sex marriage which could pave the way for its legalisation.

He told Sky News legalising same sex marriage could open the floodgates to other relationships being declared as marriages.

"Any set of arrangements can be put in place. Once you change the boundary, where do you with any sort of logic draw that boundary again?" he said.

"This is a pathway which will lead to anybody claiming whatever agenda they like, just two people, being able to legally be married in a relationship."

He likened same-sex relationships to simply friendships.

"I have an affectionate relationship with my cycling mates, we go cycling on the weekend, but that's not marriage," he said.

"The law has a place historically, culturally, across civilisations because it's there for the protection of the vulnerable".

The "vulnerable" people could include children or one half of the married couple, he suggested, while same couple wishing to be married were in it for the "gratification of individuals".

When pressed on fellow Liberal MP Tim Wilson's commitment to his same-sex partner, Mr Andrews again likened the relationship to a "friendly" one

"That's fine. I have commitments to friends; I have affectionate relationships with friends as well.

"I hope he's his (Wilson's) friend as well as his partner, if you know what I am saying".

Mr Andrews comments comparing cyclists and same-sex couples has riled some on social media and just left others in fits of laughter.

On Channel 10's The Project Carrie Bickmore took the opportunity to ask Defence Industry Minister Christopher Pyne if he was a keen cyclist. He was a walker, he replied.

"Do you think you could maybe take Kevin out for a coffee and explain to him what being a same-sex couple is all about? I think he may be a bit confused?" Bickmore asked.

"Kevin has got to make his own decisions. He's a big grown up adult now and needs to make his own decisions." Pyne said.

"I've made my decision which I support marriage equality. I'll be campaigning for a yes vote."

Cyclists? Or future same-sex couples? Who can tell? Picture: Chris Higgins Source:News Corp Australia
Cyclists? Or future same-sex couples? Who can tell? Picture: Chris Higgins Source:News Corp Australia

Attorney-General George Brandis, meanwhile, has dismissed suggestions legalising same-sex marriage could lead to polygamous unions being solemnised.

One Nation leader Pauline Hanson pressed Senator Brandis in parliament on Monday about the possibility future parliaments may amend marriage laws to appease minority groups.

"The question will be to allow same-sex couples to marry. The question is specifically in relation to couples. Two people. Not more. Two people," Senator Brandis said of an upcoming postal ballot on same-sex marriage.

"I can give you my absolute assurance that, in the event that if the plebiscite question were to be resolved 'yes', the bill that will come to the parliament will deal with couples, will deal with marriage between two people.