Others have gotten compensation from the hotel. Not knowing the details of the union dispute, the blame could lie on either side. However one thing is clear: the protesters intended to disturb the guests. It must not be an enforceable violation of law or the hotel would have been able to stop it long ago. There's no satisfactory remedy in these situations.
FWIW, this is the only hotel where I have heard of this happening repeatedly. Maybe customers should just stay away until the place shuts down and everyone loses their jobs. @:-)
Just wait until the TSA is unionized and engages in a work slowdown. We will be France for the day.
GH San Francisco had also problems with the union - I remember some signing which was much more entertaining than this waking up call...