I just spoke to someone at City of Sydney and they said there is no universal law against this but any “recent” developments (say, newer than 8-10 years or so) would “probably” have had such a clause included. You need to look at the planning consent issued for your building to see if it was prohibited under that document. If it is, you have a very strong case.
Failing that, does anyone else have any cunning plans for dealing with rogue parkers? How about keys can only be issued to residents and their resident guests? Would that work?