Lawyers for billionaire Clive Palmer have told the High Court Western Australia's border closure has overreached from protecting against the virus and instead limits freedom of movement.
Tuesday's hearing comes despite WA Premier Mark McGowan recently announcing the state would reopen its borders to all states and territories from November 14, with some restrictions remaining for NSW and Victoria.
Lawyers for Mr Palmer say the case remained relevant because Mr McGowan's announcement was "prospective and highly conditional".
In June, High Court Chief Justice Susan Kiefel remitted part of the matter to the Federal Court for trial.
Federal Court Justice Darryl Rangiah found in August the border restriction was the most effective way for WA to deal with the coronavirus.
He also accepted the border should not be reopened to states or territories with active community transmission within 28 days, or to places such as Queensland where it was unknown whether there was ongoing community transmission.
On Tuesday, Mr Palmer's lawyer Peter Dunning QC pointed to Tasmania, South Australia, ACT and the Northern Territory as being low risk for coronavirus.
He said allowing people in from such areas wouldn't heighten the risk of spread in WA.
Mr Dunning said the laws were in place to prevent the spread of COVID-19 but had overreached, questioning whether they were reasonably necessary to stop the spread.
The argument goes to whether the border closure breaches the "absolute freedom of intercourse" under section 92 of the constitution.
Chief Justice Kiefel flagged an issue with constitutional validity not applying to the border closures as they're in a regulation rather than laws, but Mr Dunning said they had the character of legislation.
Mr Palmer's team argues a "hotspot" system is a practical alternative to the border closure, substantially reducing the risk of bringing COVID-19 into the state.
WA will argue its case on Tuesday afternoon.
State attorneys-general have intervened in the case, arguing the WA directions do not breach section 92 of the constitution.
The federal government withdrew from the case in August, with Prime Minister Scott Morrison saying he didn't want to cause any "anxiety" among the WA public.
A state of emergency was declared in WA in mid-March after the state recorded its first coronavirus case in February.
It has been continually extended by the state government.
On April 4, WA police chief Chris Dawson issued directions declaring: "A person must not enter Western Australia unless the person is an exempt traveller."
Mr Palmer - whose privately held company Mineralogy has offices and staff in Brisbane and Perth, and derives most of its income from WA mining - sought permission on May 18 to enter the state but was refused.
A week later he launched legal action.
