Kate asks: I have constantly been underpaid since starting in my current position. My bosses fire anyone who questions them so I need to take this higher. Can you help?
It's every worker's right to be paid correctly every time. Your boss is bound by the conditions of either your Award or Agreement and can't undercut them (e.g. by paying you a lower amount.)
It is also your right to raise with your employer any concerns you might have about your pay - if he fires you because of it, he has acted unlawfully and you can report him.
The process with chasing up money you're owed is to firstly write a letter to your employer outlining how much you're owed and a cut of date by which you expect the money to be put into your bank account (don't ask for a cheque - cheques bounce!) Keep a copy of the letter for yourself and send it to your employer via Registered Post - it costs a bit more to do it this way but there's a record of him or her having received it. If you don't get the money by the time you specify, you can lodge a formal complaint through the relevant Government department. You don't mention what State you're working in, but if you give our Australian Unions team a call on 1300 486 466 they'll be able to tell you whether you should go the State or Federal authority.
You mention that your employer gets angry if people bring up any issues. You have 6 years to make an underpayment of wages claim, so if you feel too scared to mention it, you can chase this up when you get your next job.