The Coalition is demanding the Federal Government reveals how much revenue the mining tax has raised amid reports it has generated no revenue for a second consecutive quarter.
The Australian newspaper has today reported that none of the country's three biggest miners - BHP Billiton, Xstrata or Rio Tinto - will make payments when second quarter instalments are due next Monday.
Treasurer Wayne Swan has deflected questions about whether the tax has failed to collect any revenue, telling CNBC in Hong Kong that budget revenues generally have taken a hit in the past six months.
"It is company tax, it is resource rent tax, and it is superannuation tax.
It's across the board and it reflects the global volatility that we have seen in the economy, affecting confidence, lower commodity prices affecting incomes," he said.
The companies involved are saying little, with BHP noting the market situation has changed considerably since the mining tax was designed in 2010.
"The Australian dollar and commodity prices in particular have experienced significant volatility over this period and these have a direct bearing on MRRT payable," a company spokesman said.
The latest budget figures released last month show the Government received $1.1 billion in resource rent taxes (including both the Minerals Resource Rent Tax and the Petroleum Resource Rent Tax) between July and the end of October, but it did not provide a breakdown of the figure.
In the 2012-13 budget, the Government predicted the mining tax would raise $3 billion, although that was later revised down to $2 billion.
The Coalition has described the tax as a failure, because it is costing tens of millions of dollars to administer while not raising any revenue.
"He's supposed to be have been collecting the revenue for more than six months, [but] he's refused to tell us how much or how little he has collected," shadow assistant treasurer Mathias Cormann told ABC News.
"So what we're saying, the mining tax secrecy must stop.
People deserve to know how much or how little the Government has raised, in particular given the Government has already committed all of the money they thought it would raise and more." 'Won't be enough' The Greens have long argued for changes to the design of the tax so that it applies to more companies and more resources.
"Let's wait and see until we actually get the figures in next week, but whatever they are it won't be enough," Greens leader Christine Milne told reporters in Hobart.
"We need to raise revenue in Australia.
We need to plug the loopholes in the mining tax so that we do have the money to increase Newstart, to fund the Gonski review into education, to fund Denticare." There has been a steady recovery in the spot price of iron ore over recent weeks, prompting speculation it may help reverse the Government's budget problems.
But a spokesman for Acting Treasurer Penny Wong said: "As the Treasurer said on a number of occasions, people should be cautious about putting all their faith in numbers that are based on a day's, week's or month's spot prices for our resources." Late last year, Mr Swan announced it was "unlikely" the Government would be able to deliver a budget surplus this financial year, despite repeatedly promising to do so.
He pointed to declining tax revenues and lower-than-expected commodity prices.
Mr Swan recently wrote to some ministers, asking them to find further spending cuts given the need to pay for other expensive promises including a National Disability Insurance Scheme and an overhaul of school funding.