Plumbing licensing in NSW and Queensland
NSW. Specialist work, including electrical wiring, plumbing, drainage, gasfitting and air conditioning and refrigeration, needs a licence whatever it costs. Plumbing, drainage and gasfitting all fall into that group.
Queensland. The QBCC licenses plumbing and drainage at any value, both as a contractor licence and as an occupational licence for the person doing the work. If you subcontract to a licensed builder you need a contractor licence of the right class for your work. If you subcontract to a licensed trade contractor you may not need your own contractor licence, though occupational licences still apply.
Licensing rules change and depend on the work. Always confirm with the regulator in your state.
Sources: Checking your contractor or tradesperson is qualified (NSW Government) · When you need a licence (QBCC) · Available licences (QBCC)