New WA Liberal leader Mike Nahan has written to Bill Shorten asking for his commitment to a GST floor, saying the federal Labor leader cannot be a spectator on the issue.
West Australian MPs, both Labor and Liberal and state and federal, expressed outrage on Friday after the Commonwealth Grants Commission released its annual distribution figures, revealing WA would only get 34.4 cents in the dollar in 2017/18.
Treasury had been counting on 38 cents, so the allocation - just $2.354 billion out of a $62.74 billion pool - leaves the new Labor government with even more dire finances than expected.
But Prime Minister Malcolm Turnbull says WA will have to wait until 2019/20 for the floor, which will only be introduced after the state's share rebounds above 70 cents in the dollar under the current formula.
Dr Nahan says he is "shoulder to shoulder" with WA Labor in trying to get a better allocation for the state but wants Mr Shorten to declare his position.
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"I am confident a floor can be implemented however it does require support across the political spectrum and at a state and federal level," Dr Nahan said on Tuesday.
"Mr Shorten cannot be a spectator on this issue. He needs to tell Australians whether he supports a fairer distribution of the nation's income or whether he advocates the continuation of the unfair treatment of one group of Australians."
Premier Mark McGowan has rejected both the suggestion Mr Shorten is a sticking point and the federal government's insistence all states and territories need to agree to change the distribution formula, saying Mr Turnbull has the power to do it himself.
Meanwhile, WA Treasurer Ben Wyatt wants the Commonwealth to continue top-up payments that acknowledge the state has suffered unintended consequences of the way GST revenue is carved up.
Its lagging nature means WA's share plunged years after the mining construction boom ended and royalties fell, reaching a record low of 30.3 cents in 2016/17 and delivering a double whammy to the state's finances.
Mr Wyatt has also backed a call by WA Liberal Senator Dean Smith to conduct a Productivity Commission inquiry into the GST distribution.
