A coalition of U.S. states has accused Meta Platforms Incorporated of designing its social media and communication platform interface in an addictive and harmful way.

The coalition’s case against the parent company of Facebook, WhatsApp, and Instagram began Tuesday in federal court in Oakland, California, and is expected to last several weeks.

The 29 states accused Meta of violating federal law by improperly collecting and using children’s personal data.

The plaintiff accused Meta of designing its user interface in a way that is addictive to children and teenagers, while citing risks including anxiety, depression, suicide and other psychological harms.

The states also alleged that the social media company used features including infinite scrolling, personalised recommendation algorithms, notifications, and autoplay to keep young users glued to its platforms.

At the trial, Megan O’Neill, a deputy attorney general for California, told the eight-person jury that Meta’s social platforms interface was designed to “hook the users, hold them for as long as they can, harvest their data, and then hide the truth from the public”.

“It worked especially well for kids. Meta needed kids, and it needed to reassure the people who cared about those kids that the kids are safe,” Mr O’Neill added.

The coalition is reportedly seeking billions of dollars in penalties and changes in Meta’s business model.

Meta’s chief executive officer Mark Zuckerberg is also expected to testify as the case proceeds.

Given the nature of the case, the jurors are expected to issue an advisory verdict, while the presiding U.S. district judge Yvonne Gonzalez Rogers will determine Meta’s liability.

Earlier, a U.S. court slammed Meta with a $567 million fine over social media harm and addiction among youth and ordered it to change how young people can use its platforms.

The presiding judge in the New Mexico case, Bryan Biedscheid of the State District Court in Santa Fe, levied the largest fine against the tech giant over issues bordering on child safety.

“Although Meta is not alone in this regard, its social media platforms are a significant contributing factor to the current mental health crisis among New Mexico’s youth, established by the substantial evidence in this case,” Mr Biedscheid ruled.

“The harmful effects of Meta’s platforms on children do not stay contained by its platforms and, instead, migrate to the internet as a whole and, perhaps most concerning, to the real world and create a common, societal burden on and harm to the affected children and their families and schools, as well as hospitals and law enforcement,” the judge stated.