“Balance billing,” better known as surprise billing, occurs when a patient receives care from a medical provider outside of his insurance plan’s network, and then the provider bills the patient for the amount insurance didn’t cover. These bills can soar into the tens of thousands of dollars.

Surprise bills hit an estimated 1 in 6 insured Americans after a stay in the hospital. And the air ambulance industry, with its private equity backing, high upfront costs and frequent out-of-network status, is among the worst offenders.

Congress is considering legislation aimed at addressing surprise bills and air ambulance charges. And some states, including Wyoming and California, are trying to address the problem even though there are limits to what they can do, because air ambulances are primarily regulated by federal aviation authorities.

Here is an example of how a surprise bill might work. Before his double-lung transplant, Tom Saputo thought he had anticipated every possible outcome.  But after the surgery, he wasn’t prepared for the price of the 27-mile air ambulance flight from a hospital in Thousand Oaks, Calif., to UCLA Medical Center – which cost more than the lifesaving operation itself.

Saputo, 63, was diagnosed in 2016 with idiopathic pulmonary fibrosis, a progressive disease that scars lung tissue and makes it increasingly difficult to breathe. The retired Thousand Oaks graphic designer got on the list for a double-lung transplant at UCLA and started the preapproval process with his insurance company, Anthem Blue Cross, should organs become available.

But before a transplant could be arranged, he suddenly stopped breathing on the evening of July 7, 2018. His wife called 911. A ground ambulance drove the couple to Los Robles Regional Medical Center, 15 minutes from their house, where Saputo spent four days in the intensive care unit before his doctors sent him to UCLA by air ambulance.

He was on the brink of death, but just in time, the hospital received a pair of donor lungs. They were a perfect match, and two days after arriving at UCLA, Saputo was breathing normally again.

Much later, when Saputo opened a letter from Anthem, he discovered the helicopter company, which was out of his network, had charged the insurance company $51,282 for the flight. Saputo was responsible for the portion his insurance didn’t cover: $11,524.79.  By contrast, the charges from the day of his transplant surgery totaled $40,575 – including $31,605 for his surgeon – and were fully covered by Anthem.

In California, Democratic Gov. Gavin Newsom signed a bill in early October that will limit how much some privately insured patients will pay for air ambulance rides. Effective next year, the law, by state Assemblyman Tim Grayson, will cap out-of-pocket costs at patients’ in-network amounts, even if the air ambulance company is out of network.

Wyoming is moving to treat the industry like a public utility, allowing the state’s Medicaid program to cover all of its residents’ air ambulance trips and then bill patients’ health insurance plans. The state would then cap out-of-pocket costs at 2% of the patient’s income or $5,000, whichever is less. Wyoming needs permission from the federal government to proceed.

Ultimately, though, state authority is limited because the federal Airline Deregulation Act of 1978 prohibits states from enacting price laws on air carriers.

Congress is considering several bipartisan bills on surprise billing. One measure by Sens. Lamar Alexander, R-Tenn., and Patty Murray, D-Wash., would ban balance bills from air ambulance companies. The bill passed committee and is now headed to the Senate floor for a vote, pending approval from Senate Majority Leader Mitch McConnell of Kentucky.