It looks like Justice Gordon has found ANZ’s late payment fees to be penalties. However, this does not make them “illegal” or “against the law”. Penalties are void or unenforceable (see Andrew v ANZ), but this is as a matter of contract (including, and often in particular, principles of equity).
The word illegality has a chameleonic quality, but it is better used to describe conduct involving a breach of the criminal law (or breach of statute) — in other words, conduct contrary to law — rather than conduct that is simply ineffective at general law. (The former question can sometimes itself be difficult to determine, as recognised in Miller v Miller).
Hence the SMH is wrong to say that the Federal Court “ruled [the ANZ’s] late payment fees charged on credit cards were illegal”. The AFR is likewise technically wrong to describe them as an “illegal penalty”, although the word is there used in its more lay sense. The real description is that the relevant fees were invalid because they were penalties.
More facepalm-inducing is this howler:
It also throws out ANZ’s six-year statute of limitations, meaning anyone who has ever been charged a late fee by ANZ can potentially now claim those fees back.
How anyone could think that a “statute of limitations” could be “ANZ’s”, rather than, say, a statute enacted by a Parliament, is just … I don’t know