Liberal Senator Cory Bernardi's remarks that allowing same-sex marriage would lead to demands to legalise bestiality and polygamy have been slammed by gay rights lobby groups and politicians.
Senator Bernardi is expected to be called into Opposition Leader Tony Abbott's office today and asked to explain himself.
With Labor demanding this morning that Mr Abbott sack Mr Bernardi from his position as shadow parliamentary secretary to the Opposition Leader, senior Coalition sources say Senator Bernardi "will be spoken to" but were unsure of what, if any action would be taken.
Speaking in Parliament last night on a gay marriage bill sponsored by four Labor senators, Senator Bernardi said the push for same-sex marriage was part of an attack on "our enduring institutions".
"It is another chip in the fabric of our social mores," he said. "The time has come to ask, when will it end? If we are prepared to redefine marriage ... what is the next step?"
"The next step ... is having three people that love each other should be able to enter into a permanent union endorsed by society, or four people. There are even some creepy people out there, who say that it's OK to have consensual sexual relations between humans and animals. Will that be a future step?"
Liberal frontbencher Joe Hockey has called for a "measured and sensitive" debate and Greens Senator Richard Di Natale describing the remarks as "offensive and appalling".
Australian Marriage Equality convener Alex Greenwich said Senator Bernardi's comments were extremely predictable, and taken straight from the "American religious right play book".
"It's based on fear, not on facts," Mr Greenwich said. "There is no international example that backs up what he's saying.
"The comments are highly offensive to the tens of thousands of loving and committed same-sex couples who just want to marry."
Judy Brown, the president of Parents, Families and Friends of Lesbians and Gays New South Wales, agreed Senator Bernardi's remarks were "terribly offensive".
She said those kinds of comments did not make it easier for young gay people, who might be suffering depression and anxiety at the thought of coming out.
"[They are not suffering depression] because of the fact they're gay. Really it's just that they're treated so badly and they have to suffer all this adversity."
Deputy Prime Minister Wayne Swan called for Senator Bernardi's sacking as Mr Abbott's parliamentary secretary.
"He has made some very offensive remarks, and I think Mr Abbott should show some leadership," he said.Assistant Treasurer David Bradbury - who does not support same-sex marriage - supported Mr Swan's call.
"He should be reprimanded."
Labor MP Amanda Rishworth said Senator Bernardi had "taken the civility out of the national conversation".
"That was a very ugly comment and he should apologise," she said.
Senior Liberal frontbencher Joe Hockey repudiated Senator Bernardi's comments and called for a "measured and sensitive" parliamentary debate on same-sex marriage.
"This needs to be a measured and sensitive debate," he said. "People do have strong views, they're entitled to strong views ... but this doesn't help."
Nationals Senate leader Barnaby Joyce - who is opposed to gay marriage and civil unions - said the same-sex marriage debate was one that attracted strong views and that, "we should all be allowed to express those strong views."
Senator Joyce said he was in no position to make criticisms of Senator Boyce and her reported intentions to cross the floor.
"I would be the last person to start saying that someone crossing the floor should be punished because otherwise I would be hung, drawn, quartered and flogged," he said.
Senator Joyce crossed the floor multiple times during the Howard government era, most notably on legislation that made changes to the Trade Practices Act in 2005.
Mr Greenwich said Senator Bernardi's remarks were far removed from the views of most Australians.
"What is encouraging to us is that a strong majority of Australians reject the kind of prejudice that Cory Bernardi is trying to peddle.
"They know that this debate is about families, equality and love and, obviously, gay and lesbian Australians know we've got the majority of Australians on our side."
Mrs Brown said same-sex couples should have the same human rights as heterosexual couples.
"Our son has been with his partner for eight years ... and I just think it's an abuse of their basic human rights that they're treated as second-class citizens."
Senator Bernardi has regularly courted controversy, most notable with his commentary on Islam and multiculturalism.
In 2010, Senator Bernardi was reprimanded by Mr Abbott when he called for Australia to follow the lead of France and ban the burqa, describing it as "the most public symbol of fundamentalist Islam".
In a regular internet blog, the South Australian senator said there were supporters of fundamentalist Islam who wanted to impose sharia, or Islamic law, in Australia.