I agree with that law completely. We must get their identity no matter what. France passed that law afew months ago so I'm glad to hear that Australia is doing the same. We definitely need that law here too.
Two main reasons: I consider it a symbol of female oppression and I find it deaf-hostile. Sign languages depend on facial expressions for maximum contextual understanding.
You do realize that banning women from wearing something also qualifies as female oppression? You are falsely subscribing to the western belief that muslim women all are "forced" to be muslims, despite the fact that women maintain their muslim identities after leaving home, and the fact that massive amounts of people in non-muslim countries convert to Islam every year
Secondly, in a previous post on the topic a long time ago, I pointed out that it is an obligation in Islam to help those around you, whereas the niqab is considered by most muslims to be simply an "extra good thing" to do (whereas hijab, dressing modestly and behaving modestly, is considered obligatory for both sexes). Most niqabis would find out a way to accommodate a deaf person, be it another form of communication, or temporarily removing their niqab.