California sex offenders shouldn’t have to turn over their Twitter, Facebook or e-mail account information to police because they have a right to anonymous online speech, privacy advocates are set to tell a judge.

American Civil Liberties Union lawyers are seeking to keep a voter-approved law targeting human trafficking and sex exploitation from taking effect while they proceed with a lawsuit aimed at overturning portions of it. California law enforcement officials say tracking Internet communications can prevent offenders from preying on children.

“Possession of this information may provide enough of a head start to save a victim’s life,” California Deputy Attorney General Robert Wilson said in a court filing in federal court in San Francisco. “Having Internet identifying information, however, does not permit access to, or monitoring of, private communications.”

Proposition 35, approved by more than 80 percent of California voters last month and backed by former Facebook Inc. (FB) executive Chris Kelly, was set to take effect next year. It was put on hold by U.S. District Judge Thelton Henderson when the ACLU sued the day after the measure passed. The ACLU is scheduled to ask Henderson today to keep an injunction in place while the case is being decided.

The measure increases prison terms for sex offenders and increases reporting requirements for them. Registered sex offenders in California would be required under the law to report to law enforcement all Internet identifiers and Internet service providers they use. Registrants also would have to provide in writing any changes or additions to their Internet accounts and screen names.

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