GlenB, if you attempt to sue CASA, all you will do is trigger a CASA audit a few months after your lawsuit is dismissed.
That audit, will find numerous non compliances, after which CASA will deem you not to be a "fit and proper person" to be associated with Aviation in any form*. Your business will then bleed to death while you try to legally challenge CASAs ruling as has happened to many others.
Either start a political campaign as I have suggested or follow Dick Smiths suggestion and get out while you can.
Everything else, from tinkering around the edges, to negotiation and sweet reason, to the Administrative appeals tribunal, to the courts, to a full blown Senate review has been tried and has failed.
CASA is a parasite on the Aviation body. Your business or CASA - only one of you can survive.
* CASA willl deliver its verdict to you on Christmas Eve or the Thursday before Good Friday to maximise your pain by preventing an immediate injunctive response.