I know that illegal search and seizure, freedom of assembly and all that are pertinent here. If real, face bandana-wearing Anarchists are involved, well... I've seen some Anarchist "protests" in person that were very much not on the legal side of things. They involved destruction of public property and provoking police officers. If that's what these groups were meeting to plan, then there is some level of justification. Something in the realm of Conspiracy to Commit *insert felony here*.