Zuckerberg San Fransisco General hospital, renamed after the billionaire Facebook founder donated $75 million, does not accept any private insurance carriers—which can leave unwitting patients with tens of thousands of dollars in medical bills, Vox reported Monday report. Because of the hospital’s unusual policy, all private insurers are considered “out of network,” meaning that in some cases, they only cover a small fraction of medical costs. One woman, who suffered a broken arm, was given a $24,000 bill, and her insurance only paid about $3,800; another woman is still fighting the $31,000 she’s been asked to pay to treat a broken ankle. This system, patients say, is especially unfair to those who are transported in emergency situations via ambulance, because they have no say over where they are taken.

A spokesperson for the hospital told Vox that “It’s a pretty common thing” for hospitals not to accept private health insurance. But researchers and health-care experts rejected that claim, noting that only about 1 percent of ambulances take patients to emergency rooms that are out of network. “According to what I’ve seen, that’s unusual,” one economist said. “I’ve heard anecdotes of some hospitals trying a strategy like this, but my impression is that it doesn’t last very long.”