Calls for the state government to reopen borders have grown with South Australia opening their borders to Western Australia, Tasmania and the Northern Territory.

Premier Peter Gutwein said a reopening date would be announced on June 26 and is expected to be in late July.

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The University of Tasmania's Dr Scott Carver said reopening to state's with a low infection rate would be low risk.

"The risks get lower with state's that have had longer durations without new cases from community transmission," he said.

"The risks at the moment are low but getting it wrong has big impacts so I think everybody wants to be a little careful."

The debate around border restrictions has been further complicated by a High Court challenge from businessman Clive Palmer against WA and QLD's border closures.

Mr Palmer, who's position has been backed by the federal government, is arguing the border closure is unconstitutional as it prohibits free trade and movement between states.

He suggested the closure was unnecessary as other public health measures in the state had ensured infection rates were already falling before WA restricted travel in and out of the state.

UTAS Senior Lecturer in constitutional law Brendan Gogarty said the case has implications for all states.

"It will determine in the immediate sense the legitimacy of WA's shutting down of borders, it may also have a more long term impact on the capacity of other states to shut their own borders down," he said.

He said if the challenge is successful it would limit the ability of states to close their borders in the future.

"It will really affect the ability of the state to react in a crisis, placing an onus on them to provide clear evidence that shutting their borders down was the only way to deal with an emergency" Dr Gogarty said.

Tasmania and Queensland have both intervened in the case in support of WA.

Premier Gutwein said the Attorney General has instructed the Solicitor-General to support a State's right to impose and maintain border restrictions, in the context of the present public health emergency.

"We will be presenting a robust submission in support of the States' powers to impose these restrictions where required," he said.

If WA reopen their borders before the case is heard in the High Court it will become a moot point and the case will not proceed.

The case is expected to be heard later this month.

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