As Australian states and territories move to seal off their borders to slow the spread of COVID-19, questions have been raised over whether the extreme action is legal under our Constitution.

So far Western Australia, South Australia, Tasmania and the Northern Territory have closed borders, meaning anyone who arrives from interstate will need to self-isolate for 14 days with exemptions for essential services and health workers.

Queensland’s borders will be closed from midnight on Wednesday, while Victoria, the ACT and New South Wales remain open for now.

So, are state and territory border closures allowed?

In some circumstances, yes.

Under Section 92 of the Constitution, it states:

… customs, trade, commerce, and intercourse among the states, whether by means of internal carriage or ocean navigation, shall be absolutely free.’’

This means Australians should be “absolutely free” to move across state and territory borders.

But Anne Twomey, a professor of constitutional law at the University of Sydney, said the term ‘absolutely free’ could change during a dangerous pandemic.

“It has always been subject to an understanding that the states and Commonwealth can enact laws that protect things like public health,” Professor Twomey told The New Daily. 

Although the prospect of state border closures might appear dramatic, the measure is nothing new.

During the devastating Spanish flu pandemic in 1919, the border between Victoria and NSW was closed after a soldier contracted the disease from an infected passenger during a train journey from Melbourne to Sydney.

“The Spanish flu is the last time such an incredibly serious type of pandemic happened, so that’s a reasonable comparator,” Professor Twomey said.

“It just goes to show that in a crisis, things change.

“Most of these crises are defence issues, like in World War II. The way the High Court has interpreted the defence power is that it waxes and wanes and expands during a time of war. And in times of peace, it shrinks.”

More recently, before the coronavirus reached Australia, border restrictions and quarantine zones already existed in every state and territory to stop diseases or pests from infecting crops.

For example, interstate travellers are banned from bringing certain fruits into Queensland due to fruit fly epidemics.

How far can the border closures go?

Of all the states and territories that have introduced border closures to manage the spread of COVID-19, Queensland has the toughest rules.

In other states like Tasmania, border restrictions mean visitors must spend two weeks in self-isolation.

But in Queensland, visitors will be denied entry.

Premier Annastacia Palaszczuk said the state’s border would only remain open to freight and essential travel, and some residents who work on either side of the border.

Professor Twomey said the move was “a bit more controversial”.

“I think Queensland has gone further by saying they’re not going to let certain people in,” Professor Twomey said.

“If there is going to be a (legal) challenge, it’s more likely to be the types of laws that prevent people from coming into the state rather than laws that say you can come in, but you need to self-isolate.

“I suspect at this stage in the game, people are more concerned about protecting their health than running off to court.”