Good questions beer and aussie. Imagine if beer set up a business and employed people on an EA. Alright everythings cool. Then aussie who is a business partner of beer sets up a company that does the same stuff but says he will only employ brand new people (not existing workers from beer's business) on different workplace arrangements (ie Individual contracts). If beer and aussie have different business names, then to my knowledge there is nothing stopping this from happening.
However if beer decides to use aussie's workers in a labour hire arrangement then it is up to the workers and the union of beer's workers to demand in negotiation that labour hire be paid the same as employees.
Unless there are changes to Corporations law that does not allow the setting up of these type of company arrangements then IR law is somewhat helpless.
What IR currently prohibits is that existing workers at beer's company be moved to aussie's company and paid aussie's individual contracts (if they are inferior). Beer's workers are entitled to take their terms and conditions with them.