South Australia's planned tax on five major banks has prompted other state treasurers to swiftly get on the phone to Tom Koutsantonis.

"Yes, I've fielded phone calls from nearly all of them [about this tax]," SA Treasurer Mr Koutsantonis told reporters at a news conference on Saturday.

The SA Government said it expected the measure outlined in this week's state budget would raise about $370 million over four years, with the Commonwealth, NAB, Westpac, ANZ and Macquarie the banks it will target.

Westpac also owns the locally branded BankSA.

"We'll be passing legislation that they can't produce any extra levies on South Australians to pay for this tax," Mr Koutsantonis said.

He warned the major banks that customers would shop around for a better deal if they tried to target SA with imposts, saying the nation had 180 institutions in what was a competitive marketplace.

The SA Treasurer accused some of the banks of a hysterical reaction as they sought to protect their big profits and executive salaries.

"If a bank wants to take on the people of SA then they're welcome to," he said of the prospect of any legal challenge to the South Australian measure.

Morrison raises GST questions

Federal Treasurer Scott Morrison said the onus was squarely on the SA Government and its Treasurer over plans for the state tax on major banks.

"It's for Tom Koutsantonis to explain the legality of these measures and how they sit with earlier GST arrangements, when states agreed to get rid of taxes in return for GST revenue," he said.

"It also questions about what that may mean for GST distributions as well."

Under the SA proposal, major banks will have to pay a quarterly levy of 0.015 per cent on bonds and deposits over $250,000 — but not on mortgages and ordinary household deposits.

Mr Koutsantonis again said BankSA's assertion in the past day that it would shelve a planned 150 new business process automation team jobs in SA came out of the blue.

"I think that was news to everyone. No-one's heard of these jobs, no-one's ever heard that BankSA was planning an expansion," he said.

"All we've heard from BankSA is that they're closing regional branches all across South Australia. In fact every year over the last three years BankSA has made more profits and closed more branches."

Western Australia's Government said it was watching with interest how SA proceeded with its bank tax.