A NSW Greens proposal to ban political donations from mining companies is flawed according to Charles Sturt University (CSU) philosopher Dr Piero Moraro.

Legislation being drafted by the party would restrict miners and companies with significant state government contracts from donating money to political parties.

"The Greens are highlighting a crucial problem within Australia's political landscape, that is bribery and corporate influence over governmental policies, but they have not offered a satisfying argument to justify the specific amendments proposed," argues Dr Moraro, a Lecturer at CSU's School of Humanities and Social Sciences.

Dr Moraro's research interests include democracy and political obligation and he is also member of the Centre for Applied Philosophy and Public Ethics.

In announcing the move to increase restrictions on political donations, Greens MP Mr John Kaye said the proposal "focused on industries where there is both motivation and a track record of influence and corrupt behaviour".

Dr Moraro said the Greens may find it difficult to justify the policy to people who do not agree with the environmental agenda.

"The Greens will have to explain why they are targeting only two of those industries. In fact, one could object by asking why donations from mining companies should be banned, but not those from environmental ones," Dr Moraro said.

"If the principle is that undue influence should be stopped, then this should apply to everyone. More needs to be said to show how we can ban certain groups but not others."

Political donations from property developers or businesses in the tobacco, liquor and gambling industries are already prohibited under NSW law.

"I don't think the analogy with the tobacco industry can be used here. There is a clear connection between smoking and cancer, but we do not have that kind of evidence concerning Coal Seam Gas (CSG)," Dr Moraro said.

"I think that as long as CSG is the target only of, albeit very reasonable, suspicions of harming human health, the approach proposed by the Greens will not be justifiable."

But Dr Moraro doesn't think banning all political donations is the answer, either.

"The O'Farrell Government tried a blanket ban last year only to see it overturned by the High Court for incompatibility with Commonwealth principles. I am not sure I agree with that verdict, but it certainly sets a precedent," he said.

"Rather than banning them altogether, I think setting stricter limits for political donations could be a more viable option."