Austin v Commonwealth (2003)
Austin concerned a Commonwealth 'superannuation contributions surcharge' directed at 'higher income earners', such as State judges. Two judges, from NSW and Vic, challenged the levy.
HCA held, by maojrity, that the legislation was invalid, as it interfered with the ability of the States to discharge their functions under the principle set out in the AEU case.
All the judges in Austin, with sole exception of McHugh J, held that the two limbs of the State immunity from previous cases were better expressed as a single, overriding test.
It is therefore now possible that mere discrimination may not always be enough in itself to infringe the immunity.