Prominent economist Saul Eslake has called on the state's federal politicians to do all they can to unpick legislation that would see Tasmania lose $755 million in GST revenue by 2031-32.
The state's treasury department on Monday released a report that showed the state would lose $100 million in GST revenue in 10 years' time under a new GST sharing arrangement announced by the government in 2018.
The state is partially protected by a transitional guarantee until 2026-27 which stipulates it can be no worse off under the changed arrangement.
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Treasury forecast the state's GST revenue would decrease by $83 million in 2027-28 and rise to $100 million a year from 2031-32.
It said up until 2031-32, the state would be $755 worse off under the GST sharing deal - with 40 per cent of this covering by the transition guarantee - while Western Australia could be up to $57.5 better off.
Mr Eslake said Tasmanian federal parliamentarians should fight to have the enacting legislation changed, even if included government members crossing the floor in a vote on the matter.
He said the Productivity Commission inquiry scheduled for 2026 under the legislation should be brought forward and held immediately.
Mr Eslake said the states should demand a say in the terms of reference for that inquiry and who conducted the inquiry.
He labelled the change in the GST distribution method and transition arrangement "a corrupt bargain".
"The states agreed because they basically took the federal government's offer of a transitional guarantee," Mr Eslake said.
"The federal government based its transitional guarantee on an assumption of iron ore prices."
State Treasury in its report said it was becoming increasingly apparent that all states, with the exception of Western Australia, would be worse off under the new distribution arrangements.
Mr Eslake said Western Australia's GST share had a floor, but no ceiling on it.
Liberal senator Eric Abetz said an earlier reporting date would be helpful for Tasmania for the state budget.
"The GST arrangements over the next few years will see us once again fighting for Tasmania's interests," he said.
"GST is safe with the Liberals."
Labor's finance spokesman Dean Winter said Premier Peter Gutwein had signed Tasmania up to the arrangement and needed to fix his own mess.
"This is a deal that Peter Gutwein freely signed up to and now it's up to him to fix it," he said.
"Tasmania is going to be hundreds of millions of dollars worse off because of a deal Peter Gutwein struck."
Mr Gutwein said the GST distribution model was not in the state's long-term best interests.
"The Tasmanian Government will always stand up for our fair share of GST revenue for Tasmania," he said.
"Our position is clear - the guarantee provided by the Australian Government should be a permanent arrangement, or we should revert back to the previous model," he said.
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