Justice Gaudron states in her paper: $$The Commonwealth$$s Taxing Power and Its limits $$ Are we there yet?$(2012)$ Melbourne University Law Review $1037$:

Consideration of the Constitutionality of the exercise of that power by the Commonwealth is important, some would say essential.

You are asked to present staff training at your Law Firm on the basics of constitutional law issues in taxation. Explain the process for determining if a taxation act is constitutionally valid. You must consider issues of characterisation under s $51($ii$),$ the impact of section $55$ and the no$-$discrimination rule. You do not need to consider the impact of section $90.$