The federal opposition says the government should come clean with the public on how much the mining tax has raised to date, then immediately move to scrap it.

The comments come as one Labor MP says a budget surplus for 2012/13 is still "certainly possible", despite senior government figures describing it as unlikely.

Mining giants BHP Billiton, Rio Tinto and Xstrata are not expected to make any second-quarter payments under the minerals resource rent tax, which the government forecast would raise $2 billion in 2012/13.

The tax did not generate any revenue in its first quarter of operation and the second quarter of MRRT instalments are due next week.

Shadow treasurer Joe Hockey says the treasurer should clarify how much the MRRT has raised since July 2012.

"To facilitate passage of the MRRT legislation through the Senate, the prime minister promised monthly updates of the revenue it had collected," Mr Hockey said on Monday.

"More than six months later there is still no official update on how much or how little the MRRT has raised."

The tax was complex, inefficient, costly to administer and should be axed, Mr Hockey said.

The most recent government financial statement said resource rent taxes had reaped $1.1 billion in the financial year to October 2012, but did not specify MRRT revenue.

A spokesman for acting treasurer Penny Wong told AAP on Monday: "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."

"It's no secret that our budget revenues have already taken a big hit from the impact of continued global instability, commodity price volatility and a high dollar.

"This is hypocrisy from Mr Hockey, who repeatedly says the Liberal Party has nearly 50 policies prepared but is keeping them secret from Australians."

Opposition junior treasury spokesman Mathias Cormann said the coalition would call on the Australian Greens and independents to support the release of MRRT revenue figures when parliament resumes on February 5.

Greens leader Christine Milne said she supported greater transparency and wanted the tax to be broadened and loopholes removed.

"We do need to block the loopholes in the existing tax and expand it if we can," Greens leader Christine Milne said on Monday.

Meanwhile, Labor MP Andrew Leigh said achieving a budget surplus was still "certainly possible".

"The treasurer last year didn't rule out a surplus, just said that one was looking unlikely given what's happened to revenues," Dr Leigh told Sky News on Monday.

He said if the government enjoyed the same tax-to-GDP ratio as the Howard government it would easily achieve a surplus.

Senator Wong said the surplus remained "unlikely" but the government's stance was the "right call".