A US appeals court on Monday allowed more than 3,000 lawsuits against Meta, Google, TikTok and Snap over allegations that their platforms were designed to addict young users to proceed, rejecting the companies’ argument that federal law protected them from being sued.

The Ninth US Circuit Court of Appeals ruled that Meta and TikTok had appealed too early when seeking to overturn lower-court decisions allowing the federal litigation to continue. The panel found that Section 230 of the Communications Decency Act provides a defence against liability, rather than blanket immunity from lawsuits.

The cases, centralised before US District Judge Yvonne Gonzalez Rogers in Oakland, California, have been brought by states, municipalities, school districts and individuals. Plaintiffs allege that the companies deliberately designed products to keep children engaged, contributing to depression, anxiety, body-image problems and other harms.

Reuters reported that attorneys Lexi Hazam and Previn Warren, who represent thousands of plaintiffs, said the decision would allow a trial brought by 29 state attorneys general to proceed. “A trial is how the public finds out what Meta knew about its products’ impact on children, when it knew it, and what it chose to do with that knowledge,” they said.

The ruling came as the court rejected Meta’s attempt to postpone that multistate trial, which is scheduled to begin on Wednesday. The 29 state attorneys general allege that Meta illegally collected and used children’s data, designed its platforms to keep young users hooked and misled consumers about their safety.

Meta is facing other legal setbacks over alleged harms to children. Reuters reported that a New Mexico judge recently found the company had created a public nuisance and ordered it to pay $567 million into a teen mental health fund, following an earlier jury award of $375 million over claims that Meta misled consumers about platform safety.

A separate California case has already produced a verdict against Meta and Google. A Los Angeles jury in March found both companies negligent over the design of their social media platforms and awarded $6 million to a young woman who said she became addicted to Instagram and YouTube as a child.

The litigation forms part of wider government action over social media and children. Al Jazeera reported that France plans to ban under-15s from social media sites, while Australia has already introduced restrictions on under-16s; Britain is planning similar measures next year, with former prime minister Keir Starmer previously vowing to take “decisive” action over social media’s impact on young people.

Meta and Google have denied the allegations and said they plan to appeal, while Meta declined to comment on Monday’s ruling and TikTok did not immediately respond to requests for comment.

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