A federal judge is set to hear arguments on whether sex offenders' use of social media constitutes free speech protected by the U.S. Constitution.
Monday's hearing in San Francisco federal court comes after U.S. District Judge Thelton Henderson preliminarily blocked part of a voter-approved ballot initiative related to human trafficking.
Proposition 35 requires registered sex offenders to give authorities a list of their Internet providers and screen names.
The American Civil Liberties Union of Northern California and the Electronic Frontier Foundation sued, arguing that the rule restricts offenders' rights to free speech, due process and equal protection.
Proponents say courts elsewhere have rejected similar challenges.
The lawsuit does not affect provisions in the measure that toughen penalties on those convicted of human trafficking. Voters overwhelmingly approved the initiative last month.