The government's controversial mining tax has raised only $126 million in its first six months of operation, Treasurer Wayne Swan has announced.
The Gillard government had budgeted for the tax to raise $2 billion this financial year.
Labor has been under intense pressure to make good its promise to reveal how much money the tax is raising.
The Senate first issued demands to the government and then to the Tax Commissioner Chris Jordan and shadow Treasurer Joe Hockey forshadowed threatening to change the law to force the revenue disclosure.
The government had argued that the tax, which only applies to coal and iron ore after it was watered down from the original version after Julia Gillard became Prime Minister, was being paid by so few companies that revealing the total revenue would disclose what individual companies pay.
Treasurer Wayne Swan said it was ''clear revenues from resource rent taxes have taken a massive hit from the impact of continued global instability, commodity price volatility and a high dollar''.
''Revenues across the board are down very substantially - MRRT is a profits-based tax that raises more revenue when profits are higher and less when they are lower.''
He released a minute from Mr Jordan saying that he had ''on balance'' formed the view that it would not disclose an individual company's tax details to reveal the figure, in particular because the revenue raised in the second quarter of the 2012-13 financial year was ''substantially larger'' than the first.
In the wake of the announcement, shadow treasurer Joe Hockey suggested Mr Swan resign, labelling him the "most incompetent Treasurer in Australian history".
Mr Hockey told reporters in Sydney that Mr Swan had introduced a tax "that has caused so much pain and hardly raises a dollar".
The shadow treasurer said that the government had locked in spending that was not there and "made promises it cannot pay for"."If Wayne Swan had any self respect, he would resign," Mr Hockey said. "Just go."
Ms Gillard told reporters in Queenstown that profitability was "obviously impacted by volatility in commodity prices".
"What we said to the nation with the minerals resource rent tax is that we wanted to tax profits in our minerals sector in the most efficient way, that is, to take tax when they are at their most profitable," she said.
"There was always going to be volatility in the MRRT as a result."
Greens leader Christine Milne said the mining tax revenue "shockingly low".
The Greens have been calling on the government to not only release the revenue figures but tighten up the mining tax legislation
"The miners once again had a big win," Senator Milne told reporters in Canberra.
Greens MP Adam Bandt said he plans to introduce a bill into the lower house on Monday to close one loophole that "would mean the government did not have to give money back to the miners every time the state premiers choose to raise their royalties."
Mr Bandt said the bill would raise $2.2 billion over the forward estimates and had support from the crossbenches.
The Greens told reporters they thought Mr Swan had opened the door to Labor supporting the bill.
"We do welcome the fact that at his press conference, the Treasurer has said that he is prepared to look at other factors other than commodity prices," Senator Milne said.
Ms Gillard made renegotiating the mining tax a priority when she became Prime Minister in mid-2010, agreeing that miners could deduct state royalties from their mining tax liability. This meant that when a state raised mining royalties on iron ore or coal, the tax's proceeds were reduced.
Independent MP Rob Oakeshott has said he would support the Greens bill. He welcomed the release of the mining tax revenue figures but said structural problems with the tax had to be fixed.
"There is unfinished business in moving from a bad state-based royalty scheme to a nation-building resource rent style of taxation. Today’s figures show we are stuck in transition," he said in a statement.