The Australian Greens have declared Labor's mining tax a dud.
Greens lower house MP Adam Bandt said if it's not fixed before the May budget, there could be cuts to welfare and there won't enough funds for education reform.
"It's now clear that Labor's mining tax is a dud," he told reporters in Canberra.
The federal government on Friday revealed the 30 per cent minerals resource rent tax (MRRT) on the super-profits of iron ore and coal miners raised just $126 million in its first six months.
It was projected to generate revenue of $2 billion by the end of 2012/13.
Greens leader Christine Milne said the MRRT rate should be lifted to 40 per cent, loopholes allowing mining companies to be reimbursed for increased royalties paid to state governments must be closed and generous accelerated depreciation provisions removed.
She said those three measures could raise $26 billion over the next four years.
"It's time that we fixed this tax so we actually raise money from the big mining companies," she told reporters in Canberra.
The government says the MRRT revenue is being hit by lower commodity prices and a high Australian dollar.
Senator Milne said while commodities prices were down they were still at historic levels.
"Unfortunately Tony Abbott and Wayne Swan and the prime minister are too afraid of Gina Rinehart, Clive Palmer et al to actually take them on," she said.
Mr Bandt plans to introduce a bill to parliament on Monday to remove the royalties loophole.
"If there's any silver from today's announcement by the treasurer, it's that he has opened the door to Labor getting behind the Greens push to fix the mining tax," he said.
Greens senator Richard Di Natale said the revenue result was "hugely disappointing".
"It's a long way short of the government's projections and many billions of dollars short of the original Treasury-backed mining tax," he told Sky News.
"How are we going to pay for the things that we need in this country?"
Senator Di Natale said the low revenue was the result of a watering down of the original resources tax proposed by former prime minister Kevin Rudd.