Meta, the parent company of Facebook and Instagram, is set to defend itself in a landmark social media trial beginning Tuesday in California, where US states are seeking major financial penalties and changes to the way the company operates its platforms.

The case stems from a 2023 lawsuit filed by a coalition of states. California, Colorado, Kentucky and New Jersey were selected to represent the wider group at trial. Prosecutors are expected to argue that Meta deliberately designed Facebook and Instagram to be addictive for children and teenagers, violating state and federal laws.

The trial comes as Meta, which has more than three billion users worldwide, faces growing scrutiny over the impact of its platforms on young people’s mental health and safety.

A key early development came when Meta attempted to prevent former company employee and expert witness Arturo Bejar from testifying. US District Judge Yvonne Gonzalez Rogers rejected the request, describing the company’s effort as a “Hail Mary” attempt to eliminate a strong witness for the states.

Bejar has previously testified against Meta, including during a New Mexico case that resulted in a major legal setback for the company.

Lawyers representing California, Colorado, Kentucky and New Jersey are expected to question Bejar about Meta’s approach to safety and user growth. They are also expected to examine whether the company publicly misrepresented what it knew about potential risks associated with its platforms.

Meta has also challenged testimony from another potential expert witness, Colin Gray. In a filing submitted Monday, the company asked the judge to limit questions about so-called “dark patterns” — design features that can influence users toward choices that benefit a company.

Meta founder and chief executive Mark Zuckerberg is among the high-profile witnesses expected to appear during the proceedings. A Meta spokesperson said the company “strongly disagrees” with the allegations.

The financial stakes are enormous. During a hearing last week, an attorney representing the states said prosecutors are seeking approximately $200 billion in financial penalties. Meta had previously suggested in a court filing that the potential figure could exceed $1 trillion.

The states’ lawyer argued that Meta had calculated the larger amount “for shock value.”

Beyond financial penalties, the states are seeking changes to Meta’s apps and business practices.

Eight people were selected last week to serve on an advisory jury, although Judge Rogers will make the final decision in the case. The trial is expected to continue for about six weeks, with a verdict anticipated by early October.

Hayden Panettiere’s Death Comes Days After Court Rejects Ex-Boyfriend’s Plea to Clear Abuse Record

The social media trial is not the first legal challenge aimed at holding technology companies responsible for alleged mental health and safety harms. However, legal experts say its outcome could have far-reaching consequences for Meta and the wider technology industry.

Stanford law professor Nora Freeman Engstrom described the case as potentially the beginning of a “broader reckoning” for Meta. She said one of the central questions will be the difference between what the company allegedly knew internally and what it disclosed publicly.

Another major issue is the potential reputational damage to Meta and whether the company could face pressure to fundamentally change its products.

Vincent Joralemon, a director at Berkeley’s Life Sciences Law and Policy Centre, compared the case with the legal battles faced by tobacco companies in the 1990s.

“It really feels like tobacco in the 1990s,” Joralemon said, pointing to similarities between allegations that tobacco companies downplayed health risks and claims that Meta failed to adequately address concerns surrounding its platforms.

Dozens of US states previously sued four major tobacco companies over allegations that they concealed or downplayed the harmful effects of their products. The litigation ultimately produced the landmark 1998 settlement, which imposed financial obligations and restrictions on tobacco marketing.

According to data from the National Association of Attorneys General, tobacco companies have paid more than $176 billion under the settlement and remain obligated to make annual payments of around $9 billion.

The Meta case could similarly test whether governments can force one of the world’s largest technology companies to change the way it designs and operates social media platforms, particularly when children and teenagers are involved.