West Australian Premier Mark McGowan has labelled Clive Palmer a menace after he suggested the coronavirus pandemic was a media "beat-up".
The billionaire mining magnate will front the Federal Court on Monday to challenge WA's interstate border restrictions.
Evidence on whether the closures are constitutional is also being given by the Commonwealth, which argues WA should reopen.
A three-day trial will be heard in the Federal Court ahead of the matter returning to the High Court.
Mr Palmer has told the Sunday Times the crisis is a "beat-up" and the risk to most people is negligible, attributing most of the deaths to co-morbidities.
The premier on Sunday hit back at Mr Palmer, labelling him selfish and irresponsible and urging the federal government to withdraw its involvement in the court matter.
"He's a menace to Australia," Mr McGowan said.
"And I'd just say to the Liberal Party, don't support him in the High Court - it's wrong.
"It's irresponsible and it's playing with people's lives. Mr Palmer and the Liberal Party should back off from the High Court action."
Mr McGowan said he was confident the state's legal position was strong, adding that reopening the borders could have a dire health impact.
WA has not had any known community transmission of the virus since April 12.
"I do a lot of travelling around, I go to lots of cafes ... I'm yet to have anyone say to me 'tear down the border'," Mr McGowan said.
"Everyone says keep us safe, get our economy back within the borders and bring it down when the time is right."
Mr Palmer is arguing WA's border restrictions are contrary to section 92 of the constitution which provides for freedom of movement between the states.
Solicitor-General Stephen Donaghue QC has signalled that the Commonwealth will contribute expert evidence that targeted quarantine measures are just as effective as state border closures in managing potential COVID-19 outbreaks.
Australian Associated Press