The groups argued that the measure covers a wide range of crimes unrelated to the Internet, including misdemeanor exposure, even when the crimes occurred decades ago. They argued that people have a right to post anonymously on political forums and other websites.
"These new requirements burden the online speech of all such persons, infringe on their right to engage in lawful, anonymous speech on the Internet, and require them to reveal their membership in online groups, including groups devoted to political reform," the civil liberties groups wrote.
They sued on behalf of an anonymous 75-year-old California resident who was convicted of two sex offenses in 1986. They said the man, referred to as "John Doe," fears retaliation and social stigma if he is unable to participate in online forums anonymously. They added that the burden of documenting and reporting his Internet accounts would further deter him from participating in the sites.
"As a result, if Doe were required to disclose to law enforcement all Internet service providers and Internet identifiers he uses, he would refrain from at least some online speech due to the fear of retaliation and the burdens of reports," the ACLU and EFF wrote.
Chris Kelly, the former chief privacy officer of Facebook and a supporter of Prop 35, called the lawsuit "an attack on the very idea of sex offender registration requirements to protect kids and adults alike."
"The ACLU's claims have been previously litigated many times, and courts have repeatedly rejected their fanciful and dangerous misinterpretations of the Constitution,” he said in a statement.
—Updated at 5:00 p.m.