How can a citizen challenge a law?
Thank you for your question. Australian citizens can challenge a law in several ways.
If someone believes a law is unconstitutional or has not been validly made, they can challenge it in a court. The High Court of Australia can decide whether a federal law is made according to the rules in the Australian Constitution. If the Court finds the law does not follow those rules, it can rule that it is invalid and it will no longer apply.
Outside the court system, people can raise concerns with their representatives in the level of government responsible for a particular law. At the federal level, that means contacting the member who represents your electorate or one of the senators for your state. Representatives are responsible for making, changing and removing laws in Parliament.
Exterior of the High Court of Australia

Parliamentary Education Office (peo.gov.au)
Description
This photo shows the outside of the High Court of Australia in Canberra. The High Court is the highest court in the Australian judicial system.
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