Queensland mining magnate Clive Palmer has indicated there will be a High Court challenge against the carbon tax because he has advice the legislation is unconstitutional.

The legislation has passed both houses of Parliament and is due to come into effect in the middle of the year.

The Coalition has promised to repeal the legislation if it wins the next election.

Mr Palmer, who is a financial backer of the Coalition, first threatened to challenge the legislation last year and now says he is going to act on it.

"Our advice is that the carbon tax in its current form is unconstitutional, and that's recognised in the legislation itself when it says if it's found to be unconstitutional," he told the ABC's 7.30.

"Now, I think the constitution of Australia's much more important than having a number of lawyers or Parliament trying to slip around it.

"The constitution sets out how it should be changed, how the states should vote - the majority of Australians have a democratic right to vote."

When asked on precisely what grounds the tax is unconstitutional, Mr Palmer said: "I can only go on the advice that I'm given, and so we'll be looking forward to the challenge."

Mr Palmer says the legal action will be brought on by the companies he owns.

"The companies I own - who are large corporations - have got the rights to go to the High Court, that's what it's set up to do," he said.

"That's the country we live in - freedom of speech.

"We've all got the right to say what we think. You may not agree with it, but that's a right we fought for in many world wars."

But the Federal Government says its carbon tax legislation would withstand a legal challenge.

A spokesman for Climate Change Minister Greg Combet says the Government is confident in the legal basis for the legislation.

Mining tax

Mr Palmer also attacked the Federal Government's multi-billion-dollar mining tax.

On Wednesday the Government-dominated Senate Economics Committee released its findings into the Minerals Resource Rent Tax (MRRT) and recommended it be passed.

In line with their opposition to the tax, the Coalition and the Greens have lodged dissenting reports.

Both argue - for different reasons - the MRRT should be scrapped and the Government should go back to the drawing board.

Mr Palmer is one man the mining tax would affect.

"If you want to stop something - if you want to stop something, if you want to create unemployment, you tax it," he said.

"That's what we've done with smoking and other things. And that's what the mining tax is all about - destroying the economy, and that's what the Treasurer's doing."

He says no sector should be paying higher tax than any other sector.

"If we look at the mining particularly, it's kept this economy going, it's kept our balance of payments up," he said.

"It's made for a very high dollar because investors all over the world are giving confidence to Australia."