Scott Morrison has promised Western Australia's highest share of GST revenue is a "forever deal" despite growing agitation from other states.
The prime minister's pledge comes as new polling shows the Liberals could lose several seats in WA, which looms as a key battleground at the upcoming election.
The GST deal legislated by the federal government in 2018, when Mr Morrison was treasurer, ensures WA receives at least 70 cents for every dollar it contributes.
WA's share had previously fallen to as low as 34 cents under a carve-up which took into account the state's billions of dollars in mining royalties.
Other states, led by NSW and Victoria, have intensified calls for a revision of the deal after WA last year banked a $5.6 billion budget surplus.
But Mr Morrison has used a pre-election visit to WA to again insist there is no prospect of the deal being unwound if his government is re-elected.
He said on Wednesday the change in distribution was not a favour to WA but about fairness, which was in the national interest.
"Western Australia now, going forward, is $2.6 billion on average better off every single year in additional payments," he told reporters in Perth.
"That's some $13 billion over the next six years. That's more money for hospitals, it's more money for schools, it's more money for police and nurses and teachers.
"It's not a one-off, it's a forever deal for Western Australia that we've secured and that we've legislated and it will never, ever change under my government."
NSW and Victoria have pleaded their case for changes to the GST formula to reflect the disproportionate cost of COVID-19 on the two states.
Both have said they stand to lose billions of dollars in revenue under the existing deal.
Mr Morrison said he would continue to work closely with Mark McGowan, describing the WA Labor premier's government as "completely different" to the federal party under Anthony Albanese.
Labor is well ahead in its target seats of Pearce and Swan and narrowly in front in Hasluck, according to a poll published in the West Australian newspaper.
The incumbent Liberal MPs for Pearce and Swan, Christian Porter and Steve Irons, are retiring from politics at the election.
All three seats are held on margins of less than six per cent.
