Attorney General Christian Porter has dismissed calls for Canberra to stay out of Western Australia's borders debate, insisting the government's involvement in Clive Palmer's legal challenge against the closures is appropriate.
The billionaire mining magnate's case against WA's strict interstate border controls is before the Federal Court after being initially heard in the High Court.
Mr Palmer's argument that WA's borders should reopen is supported by the federal government, which is providing evidence in the matter.
WA Premier Mark McGowan has written to Prime Minister Scott Morrison urging the Commonwealth to withdraw its involvement, saying it makes no sense to challenge WA's position while also endorsing the NSW-Victoria border closure.
"The legal challenge, and especially the Commonwealth's involvement in it, has now become completely ridiculous," the premier told reporters on Monday.
"This nonsense has to stop and it has to stop now."
But in a statement, Mr Porter said the legal challenge was launched by a private citizen and the Commonwealth's role was limited to arguing whether border closures were constitutionally permitted in certain circumstances but not others.
"The Commonwealth did not commence these actions and cannot simply cancel them," Mr Porter said.
"If any citizen considers there are grounds to argue that their basic rights of freedom of interstate movement are being disproportionately taken from them, then they cannot be denied the right to argue that case by any premier - or any politician, for that matter."
Mr Porter said the court would be required to consider whether border restrictions were proportionate to the health crisis at specific points in time.
Two cases relating to Queensland's border closures are also before the Federal Court. The WA matter will be heard across two days starting next Monday.
Mr Palmer has accused the McGowan government of discrimination against Queenslanders.
"We haven't had any COVID-19 cases for weeks now, yet the WA Premier keeps Queenslanders out of his state," he said.
WA is also seeking a cap on the arrival of international flights after three new coronavirus cases were recorded among returning travellers from Indonesia and Doha.
A further six cases were reported on Sunday off a flight from Dubai.
Mr McGowan said there had been a steady increase in traffic at Perth Airport and the Commonwealth should ideally limit international arrivals to one flight every three days.
The government has also drafted urgent legislation which would force all returning travellers to pay for their mandatory 14-day hotel quarantine.
Parliament is not due to resume until mid-August but the premier has flagged recalling MPs for a special sitting.
More than 1100 people are currently in quarantine across five Perth hotels.
"We need to slow the flow of arrivals into Western Australia," Mr McGowan said.
There are now 12 active cases in WA, including two people from interstate. The state has not recorded a community-based infection since April 11.
WA is scheduled to move into phase five of its roadmap on July 18, removing all remaining limits on gatherings and allowing 60,000 capacity crowds at Optus Stadium.
But Mr McGowan said the date could be pushed back with authorities keeping a close watch on the latest outbreak in Victoria.
Australian Associated Press