Two large Apple shareholders are questioning the smartphone maker, saying it needs to respond to what’s seen as a “growing public health crisis” of smartphone addiction in young people, reports The Wall Street Journal. Activist investors Jana Partners and the California State Teachers’ Retirement System (Calstrs) pension fund own $2 billion worth of Apple shares. They wrote a letter to Apple asking it to help parents limit phone use through developing new software tools, and to also investigate the impact of using phones too much on mental health.

The letter cites studies that show American teenagers receive their first smartphones at the age of 10, and spend an average of 4.5 hours a day on it (excluding texting and talking times). It further states that 78 percent of teens check their phones at least hourly, with half reporting they feel “addicted” to their phones. Jana Partners and Calstrs noted that if Apple doesn’t take note and take appropriate action, its share price and standing could be hurt.

Apple’s market capitalization is nearly $900 billion, so the $2 billion stake is relatively small, making up some 0.2 percent. Still, ethical and responsible investment and the longterm payout of that is something big banks like UBS and Goldman Sachs and other investors are betting on. The Journal reports that Apple has shown willingness to use software to address the potentially negative consequences of using its phones. The investors want an easier way to impose usage limits. “Apple can play a defining role in signaling to the industry that paying special attention to the health and development of the next generation is both good business and the right thing to do,” the letter states. “The potential long-term consequences of new technologies need to be factored in at the outset, and no company can outsource that responsibility.”