California follows New York state, which passed a law earlier this year allowing parents to block their kids from getting social media posts suggested by a platform’s algorithm. Utah has passed laws in recent years aimed at limiting children’s access to social media, but they have faced challenges in court.

The California law will take effect in a state home to some of the largest technology companies in the world. Similar proposals have failed to pass in recent years, but Newsom signed a first-in-the-nation law in 2022 barring online platforms from using users’ personal information in ways that could harm children. It is part of a growing push in states across the country to try to address the impacts of social media on the well-being of children.

“Every parent knows the harm social media addiction can inflict on their children — isolation from human contact, stress and anxiety, and endless hours wasted late into the night,” Newsom said in a statement. “With this bill, California is helping protect children and teenagers from purposely designed features that feed these destructive habits.”

The law bans platforms from sending notifications without permission from parents to minors between 12 a.m. and 6 a.m., and between 8 a.m. and 3 p.m. on weekdays from September through May, when children are typically in school. The legislation also makes platforms set children’s accounts to private by default.

Opponents of the legislation say it could inadvertently prevent adults from accessing content if they cannot verify their age. Some argue it would threaten online privacy by making platforms collect more information on users.

The law defines an “addictive feed” as a website or app “in which multiple pieces of media generated or shared by users are, either concurrently or sequentially, recommended, selected, or prioritized for display to a user based, in whole or in part, on information provided by the user, or otherwise associated with the user or the user’s device,” with some exceptions.

The subject garnered renewed attention in June when U.S. Surgeon General Vivek Murthy called on Congress to require warning labels on social media platforms and their impacts on young people. Attorneys general in 42 states endorsed the plan in a letter sent to Congress last week.

State Sen. Nancy Skinner, a Democrat representing Berkeley who authored the California law, said after lawmakers approved the bill last month that “social media companies have designed their platforms to addict users, especially our kids.”

“With the passage of SB 976, the California Legislature has sent a clear message: When social media companies won’t act, it’s our responsibility to protect our kids,” she said in a statement.