A West Australian Liberals-led High Court constitutional challenge over the state's GST share will be financed by crowdfunding and attempt to force the hand of both federal leaders.
The state opposition has talked tough on the unfairness of the GST carve-up but failed to secure any changes during its eight years in government.
The party is now rattling the tin to cover the legal costs of its challenge as it continues to push for bipartisan support from Canberra to change the GST system.
Opposition Leader Mike Nahan said he tried as WA treasurer to get a better deal through negotiations with the federal Liberals and Labor, but the position in the eastern states had since "hardened".
"Our argument will be the GST is discriminatory against Western Australia and other places, both in terms of the overall allocation and the way it's administered, and we think we have a good case," he told 6PR radio on Monday.
Dr Nahan will wait until the Productivity Commission report into the GST distribution is handed down in January and says he expects it to bolster the case.
He denied he was trying to blackmail Prime Minister Malcolm Turnbull, who he said was the only federal leader fighting for a fundamental reform of GST through the Productivity Commission review.
Premier Mark McGowan said he did not want to discourage Dr Nahan, but was told the Barnett government received advice a legal challenge would fail because the current arrangements were "constitutionally sound".
"Good luck to him and if he wants to take High Court action, I would welcome him proceeding down that course," Mr McGowan told reporters.
Attorney-General John Quigley said he had received legal advice suggesting the idea was "wishful thinking".
Mr McGowan has also urged the prime minister to bring a GST solution to the Liberal state conference this weekend.
Meanwhile, federal Treasurer Scott Morrison has derided as a "sugar hit" federal Labor's plan for a $1.6 billion infrastructure fund to help WA through its GST woes.
Bill Shorten's plan, announced at the Labor state conference on Saturday, would boost commonwealth funding for WA to the equivalent of a 70 cent floor.
WA's share is currently about 34 cents.
Mr Morrison says the federal government has already provided top-ups for three years to "stop the drop" in WA's GST share.
"Bill Shorten has just made another promise like Wayne Swan made promises about setting up funds and Kevin Rudd made promises," he told reporters in Canberra.
"None of it ever happened."