Treasurer Wayne Swan has been urged to change the design of the mining tax after it was revealed it raised well below the amount of money forecast.

Mr Swan yesterday said the tax raised $126 million in its first six months, well short of the $2 billion Treasury had predicted for the year.

Mr Swan cited a huge drop in commodity prices and a higher Australian dollar for the massive shortfall.

The Greens, which have described the result as "shockingly low", say they are planning to move a bill in Parliament next week to fix some of the loopholes.

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.

Federal independent MP Rob Oakeshott says he supports the Greens but hopes Mr Swan will show some courage and take the lead.

"[It's] completely outrageous that we've found ourselves in this situation," he said.

"It has to be addressed, and I am very worried and fretting for Australia and Australian business in the non-mining sector that both major parties are either opting out - as the Liberal National Party are - or won't have the bottle to take this on in an election year in fear of mining ads mark II from a Labor government.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 1 second 3 m 1 s Rob Oakeshott talks to Samantha Hawley Download 1.4 MB

"The Greens are the only ones at the moment who are actually stumping up with a solution and facing the truth that there are some structural issues still to be addressed in this tax.

"If there's no other option, I will stand alongside them and support their position.

"I would much prefer government and in particular a Treasurer to lead on this, and when Parliament is back in session over the next couple of weeks, I hope we can get some solutions.

"The Parliament is there, and I think majority is on side, in doing what needs to be done to fix some of these loopholes and to turn this into a tax that is working in the national interest rather than against it."

Ben Mitchell from the Minerals Council any changes to the MRRT will be resisted.

Mr Mitchell says the tax was negotiated extensively with the industry and should not be changed.

"The Minerals Resource Rent Tax is just one of the three major taxes on mining. Company tax and royalties just last financial year raised $22 billion for state and federal governments.

"The MRRT is just a top up tax on top of those other very large taxes.

"There would have to be extensive negotiations with industry ... but I don't think the Government is going to be in a mind to do that.

Mr Mitchell says tax only designed to raise revenue when profits are high and is operating as it should.

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

After the release of the revenue figures yesterday, the Coalition 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.

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Prime Minister Julia 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 yesterday, 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.