Liberal senator Cory Bernardi has resigned as Tony Abbott's parliamentary secretary amid a fierce backlash over comments he made linking gay marriage to the social acceptance of having sex with animals.

Mr Abbott has described the comments as "ill-disciplined" and has accepted Senator Bernardi's resignation.

"They're views I don't share," the Opposition Leader told reporters in Canberra.

"They're views that I think many people would find repugnant.

"I had a conversation with Senator Bernardi [and] as a result of that conversation, he offered his resignation and I've accepted his resignation.

"I think it's pretty clear that I have sent a very strong message to every member of the team that ill-discipline is unacceptable.

"I think it's pretty clear that if you want to freelance, you can do so on the backbench," he said.

During a Senate debate last night Senator Bernardi said the push for same-sex marriage was coming from "radicals" who were determined to overturn the social fabric of Australian society.

And he questioned where the campaign would end, if society was prepared to redefine marriage based on the "latest criterion" that it should be allowed irrespective of gender.

"The next step, quite frankly, is having three people or four people that love each other being able to enter into a permanent union endorsed by society - or any other type of relationship," Senator Bernardi said.

"There are even some creepy people out there... [who] say it is OK to have consensual sexual relations between humans and animals.

"Will that be a future step? In the future will we say, 'These two creatures love each other and maybe they should be able to be joined in a union'.

"I think that these things are the next step."

Sorry, this video has expired Watch Cory Bernardi's comments in the Senate

Speaking on ABC Radio this morning, Senator Bernardi was not backing down.

"We've already had complaints from those in the polyamorous community about [how] this will discriminate against them... these people will continue to advocate for these causes and I think if we're going to redefine marriage... there will be another call to include a broader system," he said.

"And I don't know where it will end."

This afternoon, Senator Bernardi released a short statement saying had resigned "in the interests of the Coalition".

"My focus is now on directing my time and energy to representing the people of South Australia as a Liberal senator."

'Misrepresented'

His comments were swiftly condemned by the Government, the Greens and even some of his Liberal colleagues.

"Senator Bernardi is entitled to say what he likes, but the fact is that his views are extreme, they are hysterical, they're not the views of the mainstream Australian society - let alone of the Liberal Party," Liberal frontbencher Malcolm Turnbull told ABC News 24.

"[The argument that] if that gay couple that have been living together for 30 years are allowed to term their relationship a marriage, that will lead to people having sex with animals and wanting that to be described as a marriage - that is so bizarre.

"I want my constituents to know that I disassociate myself from those views."

But former South Australian senator Nick Minchin has defended the controversial Liberal, saying he cannot see why Senator Bernardi had to resign.

"His remarks have been quite mischievously and deviously conflated and misrepresented, and I think any fair and objective reading of what he was actually saying would lead the reasonable person to conclude that his was a perfectly proper defence of the traditional definition of marriage," Mr Minchin told ABC Radio.

"I certainly... see no reason for him to resign."

Mr Minchin says the speech was a "proper and appropriate" defence of the Liberal Party's long-standing support for the traditional definition of marriage.

Sorry, this video has expired Malcolm Turnbull speaks to Lyndal Curtis on ABC News 24

'Tin ear'

Mr Abbott has announced that NSW senator Arthur Sinodinos will replace Senator Bernardi as parliamentary secretary to the leader.

South Australian MP Jamie Briggs will become the Opposition's parliamentary secretary for families.

Senator Sinodinos says while his heart goes out to Senator Bernardi, the comments did show a lack of discipline and a "tin ear" when it came to community views.

"While we have free speech, we always have got to be careful about the implications of our remarks and I think to some extent, that was seeking to take something to a conclusion that I don't think was appropriate," he said.

Senator Sinodinos says part of his new job will involve picking up early warning signs of any problems within the Coalition and providing "wise counsel" to the Opposition Leader.

"At the end of the day, the (opinion) polls are looking at a change of government and so (Mr Abbott's) role is to keep rolling out alternative policies as well as keeping the Government accountable," he told ABC News 24.