FWIW, if any Australians are reading this : Union fees are tax deductible. And your employer doesn't need to know your part of the union until absolutely necessary. Seriously, I know there is a lot of bad press about unions because of a few arseholes, but they are necessary and you may find you need them the longer Abbott is in power.
Just to add, union dues and initiation fees are also tax deductible in the U.S.; however, you can only deduct the amount above and beyond 2% of your AGI.