The Turnbull government is staring down claims there is a $2 billion "black hole" in the revenue its new bank tax will raise, after federal Labor cited figures from the big four banks and industry estimates to attack the levy.

Labor has said it will back the new tax, which is supposed to raise $1.6 billion in its first year, and $6.2 billion over four years.

The ALP has hammered the government over its revenue forecasts after Westpac, Commonwealth Bank, ANZ and NAB released estimates that suggested $965 million would be raised, after tax, in the first year of operation. Macquarie, the only bank yet to release an estimate of what it will pay, is not expected to make up the shortfall.

However, the government believes the gross revenue figure of about $1.4 billion from the big four banks, when combined with Macquarie's yet-to-be-revealed figure, means the $1.6 billion revenue estimate is on track.

The banking industry has argued both publicly and privately that the government's revenue estimates are wildly optimistic, that the tax design is fundamentally flawed and that the new 0.06 per cent levy should apply to major foreign banks that have smaller subsidiaries operating in Australia. It has also said the industry has been unfairly targeted.

The government has ruled out the inclusion of foreign banks in the levy.

The banking industry is also pushing for a sunset clause to be inserted into the so far unreleased legislation that would see the levy expire when the federal budget returns to surplus.

The legislation to establish the levy has been a closely guarded secret, with the five banks affected required to sign non-disclosure agreements before seeing it. The banks say they have not been given modelling they were promised by the Treasury at a meeting two weeks ago.

Amid growing questions about the levy's revenue, Labor treasury spokesman Chris Bowen accused the government in question time of having a "$2 billion black hole" in its revenue estimates.

"The big four banks have reported to the Australian Stock Exchange that they will pay $965 million over 12 months for the bank tax," he said. "Isn't it the case that this falls well short of the 12-month figure in the budget of $1.6 billion for the bank tax? When will the Treasurer admit, just admit, that he has a $2 billion black hole?"

Treasurer Scott Morrison fired back, accusing Mr Bowen of doing the major banks' bidding.

"The numbers are set out in the budget papers," he said. "It may come as news to the shadow treasurer, but banks don't get to decide how much tax they pay - the ATO works that out."

"I cast no aspersions on the banks ... they are making estimates, statements that I assume are fully accurate from their perspective.That's what they are required to do."

The legislation to set up the levy, which is due to begin operation from July 1, 2017, is expected in Parliament next week.

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