In the protest world, they're called "SLAPP" suits. And as acronyms go, SLAPP is pretty descriptive — "Strategic Lawsuits Against Public Participation."
SLAPP suits are a strategy used primarily by corporations or developers to intimidate individuals to prevent them from participating in public protests. Or, more bluntly, to shut them up.
What makes the suits unique — and effective — is that most are filed against individuals, not groups or local governments that may have the wherewithal to mount a legal defense.