Overturning the ban on Australians travelling overseas could have resulted in every potential traveller being issued their own travel ban on a monthly basis, the Full Court of the Federal Court says.
The court on Tuesday dismissed a challenge from lobby group Liberty Works to the restriction, imposed due to the coronavirus pandemic.
The think-tank challenged the ban after one of its employees could not get an exemption to travel in late 2020.
Apart from the recent opening of the New Zealand travel bubble, people seeking to travel overseas have since March 2020 had to get a special exemption from the Department of Home Affairs.
LibertyWorks, which seeks more individual rights and freedoms, had argued the biosecurity act didn't allow Health Minister Greg Hunt to subject a group to a particular measure if that measure could also be applied to a single person under the chief medical officer's powers.
If that were so, no measures that could be applied to individuals could be applied on a broader scale "no matter how grave the emergency facing the country", the court said.
It said there was force in the Commonwealth's submission that LibertyWorks's model would "eviscerate" the health minister's powers.
"It would at least emasculate it," the court said.
"And it would frustrate Parliament's clear intention in enacting the emergency powers."
The interpretation could also mean the only way to prevent or reduce the risk of contagion from Australians travelling overseas would be by making a human biosecurity order on every potential traveller.
Each order would last 28 days, would need to be read out to each individual and couldn't be made until reasonable steps were taken to inform each individual of the risk posed to the health of the individual and the public by human disease, the court said.
A right to have the Administrative Reviews Tribunal review the order would also apply.
Having regard to all that, the court said it "defies belief" that Parliament intended such a scheme when passing the biosecurity act.
"It may be accepted the travel restrictions are harsh," the court said.
"It may also be accepted that they intrude on individual rights.
"But Parliament was aware of this."
The act allows the health minister to make an order he's satisfied is necessary to prevent or control the disease's spread to another country.
Rather than travel bans, LibertyWorks suggested disinfecting outgoing freight and mail and banning cruise ships could suffice.
That was rejected by the court.
Such measures might have a role to play but they were unlikely to achieve the purpose for the law in the first place, it said.
LibertyWorks, which organises the annual Conservative Political Action Conference Australia or CPAC Australia, was ordered to pay the government's costs as agreed or taxed.