A high-stakes legal showdown is underway in California Tuesday, with potential to change the face of social media.

Opening arguments began in the U.S. District Court in Oakland, where 29 states are part of a federal lawsuit filed against Meta, claiming Facebook and Instagram are engineered to deliberately addict children and teens while hiding the known mental heath risks.

The lawsuit also accuses Meta of harvesting data from users under 13, without parental permission.

The states are demanding Meta dramatically change its algorithm, including by placing a ban on infinite scrolling and auto-play.

Meta denies the allegations, pointing to its newly introduced restricted "teen accounts" as evidence, they say, of an on-going commitment to safety.

Meta CEO Mark Zuckerberg and Instagram head Adam Mosseri are both expected to be called as witnesses in the trial, which is expected to last four to six weeks.

RELATED STORY | Court orders Meta to pay $567 million to address kids' mental health and safety on its platforms

This case is separate from another recent landmark trial that focused on Meta's impact on young users.

In March, a jury in New Mexico found Meta was harming kids' mental health and had broken the state's consumer protection laws.

The court ordered Meta to pay $567 million, most of which would be used to pay for health and treatment services for affected youths.