The Coalition has hit back at moves to ban political donations from tobacco companies, with its MPs lining up to argue the firms are breaking no laws and "can donate to who they like".

Labor stopped accepting donations from cigarette companies in 2004, but the Coalition has been given $1.7 million since that time.

Greens leader Bob Brown will introduce a bill in the Senate designed to prevent tobacco companies donating to political parties or candidates, saying the donations influence policy.

The Government is legislating to mandate plain, unbranded cigarette packets to make them less attractive, but Opposition Leader Tony Abbott has said he thinks the move may be counter-productive.

The legislation has split the Coalition, with at least two members reported as threatening to cross the floor and vote with the Government.

A parade of Coalition backbenchers fronted reporters outside Parliament this morning, saying that because tobacco is a legal product, donations from tobacco companies should be legal as well.

Senator Chris Back says if the Government thinks the product is so bad they should move to ban it altogether.

"I think it represents the first instance anywhere that a company or a group of companies cannot market their own product under their own brand," he said.

"I don't believe that plain branding will have any effect at all on people smoking."

He said Senator Brown should "go back and have a good, long look at his own motives" in his bid to ban the donations.

But Senator Brown says "we need to clear the air of tobacco smoke pollution" in Parliament House.

"The Coalition should show its empathy and sympathy with the thousands of Australians dying each year because of big tobacco and agree to pass this legislation when it comes up in the coming months," he said.

Nationals MP Darren Chester says if corporations are accused of having influence on the Coalition, unions should be held to account for influencing Labor.

"Right now the big tobacco companies are legal entities and they have every right, in our democracy, to make a donation to whatever political party they want," he said.

"They are legal entities and they are making a decision to donate to a political party, and as long as they are disclosed among the legal parameters I don't have a problem with that."

He said the bigger debate is whether donations should be banned altogether and political campaigns be funded from the public purse.

And Liberal MP Stuart Robert said: "Donations are able to be taken as long as they are declared and in line with the law."

Independent MP Bob Katter, meanwhile, says he will not support the plain packaging legislation, describing it as a sign of a nanny state.

"There is a rampant wowserism in this country. We fought an election campaign and got a record majority [on] two issues - one of them was freedom, the issue of freedom," Mr Katter said.

"This is rapidly becoming the most restrictive society on Earth."