The Albanese Government risks losing "every seat in WA" if it changes the state's lucrative GST deal, WA Treasurer Rita Saffioti says, amid calls from independent economists to review the agreement.

Under the current deal, the Commonwealth gives WA a minimum of 70 cents for every dollar of GST, with that figure rising to 75 cents in 2024-25.

Prior to a top-up arrangement introduced by then treasurer Scott Morrison in 2017, WA's share had slumped to 30 cents in the dollar.

The most recent outlook estimated the revised agreement would cost the federal government about $39 billion over a decade.

But economists Saul Eslake and Chris Richardson independently reviewed the plan and concluded the deal will actually cost about $50 billion over that time period.

The reviews put pressure on the Productivity Commission to reconsider the top-up system when it reviews the deal in 2026-27, especially given WA's strong financial position.

The state is forecasting a $3.7 billion surplus for the current financial year.

Political suicide to change GST

Ms Saffioti vigorously defended WA's GST deal at a Chamber of Commerce and Industry breakfast in Perth on Tuesday.

"I don't think any government will, to be honest, politically it just would not work.

"They would basically, I think, lose every seat in Western Australia."

Ms Saffioti said the state had to consistently prove it was worthy of its GST share.

"In relation to the Productivity Commission review, we will continue to work to better prove our case in relation to the formula itself," she said.

'We need to continually prove that we are a very high-cost state to deliver services."

GST 'fairness fighters'

In May 2023, former Premier Mark McGowan announced the government would spend $1.6 million to beef up a team within the Treasury department dubbed GST 'fairness fighters'.

"I can imagine them out there in the jungle," he joked in parliament at the time.

He said the funds would employ three full-time staff to prepare "substantial" and "well-researched" arguments to fight against any review of GST distribution.

"If we did not do this and something unexpected or catastrophic happened, everyone would say, 'Why didn’t you do this?', so this is an insurance mechanism," Mr McGowan said.

"It is also in place to counter any of the arguments put by the states that are most aggrieved by it. New South Wales, Victoria, Tasmania, South Australia and the Northern Territory are really the big winners out of the GST distribution.

"They may seek to put submissions in; perhaps all the other states will join forces to put submissions in."

Dirty deed done dirt cheap

Mr Richardson said the estimate of $39 billion was conservative and relied on an assumption of a collapse in the price of iron ore.

"It was a dirty deed that, when initially it was done, they thought it would be dirt cheap," Mr Richardson said.

"That requires a very large drop in commodity prices to happen, an unrealistically large drop in prices of things like iron ore.

"When you put in more realistic assumptions, the cost of this deal grows well above the latest official estimates."

Mr Richardson said the deal is "magnificent" for the WA Government.

"I understand why West Australian politicians and West Australian residents wouldn't be keen to see this deal undone, but it is a massive mistake," he said.

"It's not that the other states lose, it's that Western Australia wins at the expense of Australia."

'Not in the national interest'

Mr Eslake's report is blunt in its assessment of the GST deal, calling it "the worst public policy decision of the 21st century."

"It is Federal politicians, of both political persuasions, who deserve blame for failing to see through these arguments, and for elevating narrow political calculations above the requirements of good public policy, and the national interest," the report says.

"Western Australia finally found its man in Scott Morrison, as treasurer in the Turnbull Government, a government which had five Western Australians in its cabinet."

WA Liberal Leader Libby Mettam called on Premier Roger Cook to seek a written agreement from the federal government promising it won't backflip on the deal.

"There are issues of trust and Western Australians deserve a written ironclad guarantee that Labor's position will not change on the GST," she said.

Mr Albanese and Treasurer Jim Chalmers have repeatedly vowed not to unwind the arrangement.

Speaking to the ABC on Sunday, shadow treasurer Angus Taylor said raising the GST was not his focus.

"Raising the GST in the middle of a cost-of-living crisis is not something that a Liberal is going to support. Let’s be clear about that," he said.