Clive Palmer has been denied entry to Western Australia as the state government remains adamant interstate borders will remain closed for months.
Mr Palmer wanted to visit WA for meetings with businesspeople, Senator Mathias Cormann and potential 2021 state election candidates for his United Australia Party, but was knocked back.
A spokesman told AAP he had commenced a High Court challenge to the border closure and would cite a section of the constitution that stipulates trade between states must be free.
Mr Palmer accused Premier Mark McGowan of "denying Western Australians jobs and prosperity" by refusing to open borders.
"He risks economic shutdown with his gestapo tactics," the Queensland-based billionaire said in a statement.
Mr McGowan said he endorsed the police commissioner's decision not to deem Mr Palmer exempt from the ban.
"He's made it on proper grounds and with the correct purpose behind it, which is to protect the health of West Australians," the premier told reporters.
"If Mr Palmer doesn't like it, he's subject to the law just like everyone else."
Mr McGowan reiterated WA's interstate borders would likely remain closed for months.
After batting away "bullying" from NSW Premier Gladys Berejiklian over the issue earlier this week, citing the Ruby Princess debacle, Mr McGowan said WA's eighth straight day of no new coronavirus cases was in contrast to the nation's most populated states.
"And they continue to have outbreaks, whether it's in meatworks or McDonalds," he said.
"Western Australia has been a world leader here - let's keep it that way."
Meanwhile, Mr McGowan remains under pressure to fully reopen intrastate travel after WA's 13 regions were slashed to four vast areas on Monday.
State Liberal leader Liza Harvey said it was nonsense Perth residents could cram on to public transport but not visit northern regions or the Goldfields.
"Every day the premier dithers, another West Australian small business closes its doors," Ms Harvey said.
"Our tourism industry is on its knees."
Mr McGowan said remaining intrastate restrictions were being reviewed.
"I know a lot of communities would like us to do more and as soon as we can, we will," he said.
"It's not far away, assuming we continue to have low levels of infection.
"I just ask everyone to bear with us."
WA's active COVID-19 cases remain three.