Treasurer Wayne Swan has revealed the mining tax raised just $126 million during its first six months of operation, prompting calls for his resignation.

He says the figure was only provided to him by the Tax Office yesterday, and he released it publicly in the interests of transparency.

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"The huge drop in commodity prices in the second half of last year had a dramatic impact on MRRT (Minerals Resource Rent Tax) revenues," Mr Swan told reporters in Brisbane.

"Indeed, the huge drop in commodity prices and the higher Australian dollar had a huge impact on all of our profits-based taxes."

In the 2012-13 budget, the Government predicted the mining tax would raise $3 billion, although that was later revised down to $2 billion.

Mr Swan had previously rejected calls to release the revenue figures, citing legal advice that it would be in breach of the privacy provisions of tax laws.

Yesterday, he provided written advice from the Commissioner of Taxation, Chris Jordan, who says he has formed the view that the disclosure of the total revenue figure for the first two quarters would not breach those provisions.

"In doing so I took into account a range of factors, including the total amount of the instalments, particularly the fact that the second instalment was substantially larger than the first," Mr Jordon wrote.

He also says he took legal advice from the Australian Government Solicitor.

Mr Swan says there has been a partial recovery in commodity prices over recent months, suggesting that revenue collections over the next two quarters would be higher.

'Dog's breakfast'

The Coalition has described the tax as a "dog's breakfast" and called on Mr Swan to stand down as Treasurer.

"If Wayne Swan had any self-respect, he would resign. He is totally incompetent," shadow treasurer Joe Hockey told reporters in Sydney.

Figures provided by the Tax Office show it has cost tens of millions of dollars to administer the new tax. Mining companies are reportedly spending a similar amount to comply with the new arrangements.

Shadow assistant treasurer Mathias Cormann says the tax has been bad for the economy and Mr Swan should take responsibility.

"Any chief financial officer in a publicly listed company that came in 90 per cent below his revenue target on a key measure like this would have to quit his job," he told ABC News Online.

"Wayne Swan is personally responsible for this mess and he should seriously consider his position.

"(The tax) has raised $126 million over six months, which is much, much, much, much less than he said it would raise. And of course in the meantime, he has spent billions of dollars that he thought it would raise."

Sorry, this video has expired Hockey attacks Swan over mining tax revenue

'Shockingly low'

Independent MP Rob Oakeshott says it is clear there is "unfinished business" that needs to be fixed.

"The Treasurer and Prime Minister must immediately renew negotiations in a sensible way with the states on comprehensive tax reform and make this mining tax issue a priority in those discussions," Mr Oakeshott said in a statement.

"Either that, or use the Parliament or budget to close some loopholes and make the tax work better."

The Greens have described the revenue outcome as "shockingly low" and are demanding the Government make changes to the design of the tax.

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They argue state royalty increases should not be refunded by the Commonwealth, that the tax rate should be increased to 40 per cent, and that the coverage of the tax be broadened to include other minerals.

"This is a Government that said it was prepared to take on the mining industry, but now what we've seen is that the miners once again had a big win over Julia Gillard and Wayne Swan in the negotiation of this tax," Senator Milne told reporters in Canberra.

Ms Gillard renegotiated the mining tax with the three biggest miners - BHP Billiton, Rio Tinto and Xstrata - soon after she took over from Kevin Rudd as Prime Minister in 2010.

Speaking to reporters in New Zealand, Ms Gillard defended the policy, saying it was designed to tax minerals in the most efficient way.

"There was always going to be volatility in the MRRT... but I still think it's absolutely fair that at the peak of the profit cycle, Australians see tax from mineral wealth that is dug out of the grounds we all own and the grounds we all share," she said.