Surprise billing has become a serious issue among healthcare consumers who are frequently stuck with a bill for thousands of dollars after receiving care. The practice of surprise billing is largely caused by wide fluctuations in healthcare prices around the country for services.

Another reason may be that some hospitals have their own policy of keeping all private insurers out of network.

That’s the case with Zuckerberg San Francisco General Hospital, the largest public hospital in San Francisco, Vox reported. By not participating in the networks of any private health insurers, patients who are privately insured are left with sky-high medical bills if they receive care there.

As the city’s largest trauma center, about one-third of all ambulances bring patients there, meaning consumers likely don’t have the ability to determine if they will receive out-of-network care before they arrive at the hospital.

According to the hospital, which was renamed after Facebook founder Mark Zuckerberg donated $75 million, its practices are not unusual and aim to serve those covered by public insurance. Others disagree, arguing most other public trauma centers accept several private health insurance plans.

The billing practices were uncovered as part of Vox’s ongoing investigations into ER medical bills.

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