Mandatory to disclose current salary to progress application. Australia.

Question for Australians. Got asked by a recruiter that their client wants to know my current salary where I am. I refused to answer and politely advised them I consider that private information. They tell me it’s mandatory by their client to progress my application for the role. Is this legal in Australia? I understand asking for your current salary is not illegal but making it mandatory to actually apply and without giving reason what they do with that information?