Back in 2012, Californians decided to double down on punishment for registered sex offenders. Proposition 35 required sex offenders to provide law enforcement with a list of their "Internet identifiers," which could include email addresses, Facebook accounts, or even a user name on an obscure online forum. (Note that Prop. 35 was largely about increasing penalties for human trafficking; the part about sex offender Internet accounts was barely ever mentioned.) Failure to provide law enforcement with written notice of additions or changes to these identifiers, within 24 hours, would subject the offender to criminal penalties.
On the day the proposition took effect, several registered sex offenders sued to block the law's enforcement on First Amendment grounds and on the ground that it was void for vagueness. The district court enjoined enforcement and the Ninth Circuit affirmed.