Determination of Head of Legislature Power under constitution
The general principles to be applied in determining whether a law is with respect to a head of legislative power are well settled. It is necessary, always, to construe the constitutional text and to do that "with all the generality which the words used admit". The character of the law must then be determined by reference to the rights, powers, liabilities, duties and privileges which it creates. The practical as well as the legal operation of the law must be examined. If a law fairly answers the description of being a law with respect to two subject-matters, one a subject-matter within s 51 and the other not, it is valid notwithstanding there is no independent connection between the two subject-matters. Finally, as remarked in Grain Pool of Western Australia v The Commonwealth, "if a sufficient connection with the head of power does exist, the justice and wisdom of the law, and the degree to which the means it adopts are necessary or desirable, are matters of legislative choice.
 R v Public Vehicles Licensing Appeal Tribunal (Tas); Ex parte Australian National Airways Pty Ltd  HCA 15; (1964) 113 CLR 207 at 225-226; Grain Pool of Western Australia v The Commonwealth (2000) 202 CLR 479 at 492 .