California Governor Gavin Newsom has signed AB 1394, a law that would punish web services for “knowingly facilitating, aiding, or abetting commercial sexual exploitation” of children. It’s one of several online regulations that California has passed in recent years, some of which have been challenged as unconstitutional.

Newsom’s office indicated in a press release yesterday that he had signed AB 1394, which passed California’s legislature in late September. The law is set to take effect on January 1, 2025. It adds new rules and liabilities aimed at making social media services crack down on child sexual abuse material, adding punishments for sites that “knowingly” leave reported material online. More broadly, it defines “aiding or abetting” to include “deploy[ing] a system, design, feature, or affordance that is a substantial factor in causing minor users to be victims of commercial sexual exploitation.” Services can limit their risks by conducting regular audits of their systems.

As motivation, the bill text cites whistleblower complaints that Facebook responded inadequately to child abuse on the platform and a 2022 Forbes article alleging that TikTok Live had become a haven for adults to prey on teenage users. Prominent supporters include the child-focused nonprofit Common Sense Media. But like many other online regulations, it raises questions about unintended side effects, including encouraging sites to under-enforce rules to avoid “knowingly” encountering illegal material or over-enforce them and remove innocuous content. Techdirt’s Mike Masnick likened the bill to “a kind of mini-California FOSTA,” referring to the widely criticized federal law that punished web platforms for content advertising sex services.

Tech industry trade associations TechNet and NetChoice raised concerns about the bill, with NetChoice urging Newsom in September to veto it. “Unfortunately, in the legislature’s desire to decrease CSAM online it passed a bill that imposes liability in a manner inconsistent with the First Amendment,” said NetChoice vice president and general counsel Carl Szabo.

Even so, AB 1394 has gotten less attention than a number of other California internet laws. Elon Musk’s X (formerly Twitter) sued in September over AB 587, which requires sites to formulate and post plans for addressing hate speech. And NetChoice, which issued successful challenges to Texas and Florida social media moderation bans, convinced a judge to block the California Age-Appropriate Design Code Act as unconstitutional last month. The organization did not immediately confirm to The Verge whether it’s planning a similar challenge to AB 1394.