The Employment relations (Triangular Employment) Amendment Act is a more complex piece of legislation which will no doubt be tested by case law, but fundamentally it allows for a third party to be named in a personal grievance.
Whilst who will be considered third parties will need to be established by case law broadly you can think team members hired through an agency on short term temping assignments as potential groups of employees who may fall into this category. Read more about the Act and what it means here: