I don't disagree shark patrol.
The PA announcement is a ban. The FWA allows an employer to reduce pay because of bans, regardless of what the ban might be, but it also means a worker can complete other work and still get paid for it.
If part of your job as a pilot is to say "this is your captain speaking etc etc", and you chose to not say it for the purposes of PIA then it leaves it open for QF to deduct pay proportional to the ban taking place.
It is open for QF to not accept the ban altogether though. Again the reasons behind that could be disputed in FWA