I’m not disagreeing that there’s a basis for challenging the determination. But I would have argued that it doesn’t meet the requirements of the Act because there are potentially other methods which are less intrusive to achieve the same result. The declarations under the biosecurity act can only be those which are absolutely necessary (or words to that effect).
The Biosecurity Act has always allowed the minister to make a declaration, which could include banning something or someone coming to australia if the risk warranted. I would have thought that by implication, the ability to make such a declaration was provided by parliament with full knowledge of the interaction of other acts? If you didn’t allow the minister to make declarations under the act, and if there was no penalty associated with breaching those declarations... what’s the purpose of the act?
The Minister can make as many declarations as they want. Whether they are valid is another question. Executive declarations have a long history of being challenged as ultra vires, and those challenges can succeed. The executive likes to take the easy path, which is to govern by executive declaration, rather than be subject to the scrutiny of parliament. Judicial review checks the exercise of the executive power in that way.
But as I explained in my first post, I harbour considerable doubt as to whether a challenge would succeed. The courts typically give governments latitude during public health emergencies.