Opening arguments kicked off Tuesday in what could be Meta’s most consequential legal fight yet over youth safety and addiction. If Meta loses the case, it could fundamentally change how the company’s social media platforms operate.

Of the thousands of lawsuits Meta faces over child safety on its platforms, none may be more consequential than one going to trial this week in California.

This week a trial kicks off in federal court, where four states—California, Colorado, Kentucky and New Jersey —argue that Meta misled the public on the harms of social media to young minds.