WASHINGTON — Congress is trying to fix one of the most glaring market failures of the American health care system, but a high-powered fight between wealthy industry groups is threatening to kill any changes and leave patients vulnerable to massive surprise medical bills.

Lawmakers want to prevent doctors and other specialists from charging backbreaking fees to desperate patients who have no capacity to negotiate or refuse care. But the main proposed fix has caused a massive lobbying backlash from doctors and hospitals working to kill the bill despite support from insurance companies and consumer advocates.

Now fears are growing that the PR and lobbying battle could sink the unsteady bipartisan consensus and leave patients exposed.

“I am concerned,” said one Republican aide. “It’s been a big blitz, a really big blitz.”

Before it left for summer break, the Senate drafted, but did not end up voting on, a bipartisan bill to end surprise medical billing — the situation when someone goes to a hospital within their insurance network, only to be hit with huge bills afterward because people working at the hospital are out of network.

Though it is widely denounced as unethical, billing unsuspecting emergency room patients who can neither foresee nor prevent the expense has proven to be a lucrative business. A recent Journal of the American Medical Association study of millions of hospital records found that over 40% of emergency room visits end in patients getting out-of-network bills.

The problem is how to fix it. Both the House and Senate have bills ready to go to end surprise billing and President Donald Trump has said it’s a top priority (though the administration has not released details on what kind of legislation it wants). Both bills in Congress would force insurance companies to cover out-of-network costs for in-network ER visits. The question is how much should care providers (ER doctors, anesthesiologists, radiologists, etc.) be able to charge the insurance companies?

This is what the industries have gone to war over.

Doctors and hospitals have mobilized against the Senate bill because it ties doctor fees to the median in-market rates. A shadowy group called Doctor Patient Unity spent August running a multimillion-dollar ad campaign attacking the bill in the states of senators up for reelection in 2020.

One ad from another group, Physicians for Fair Coverage, warns that “big insurance companies want a one-size-fits-all approach that lets them decide what they’ll pay doctors for your care,” and that this will make it harder for patients to get access to top doctors.

Hospital groups are also using insurers as a proxy for attacking the legislation. “The same people who brought us high deductible plans and narrow networks now expect patients to trust them to solve the surprise billing crisis,” wrote Federation of American Hospitals President Charles Kahn.

When it comes to legislation before Congress, doctors and hospitals have traditionally been extremely successful at getting their way.

“I’m very worried. There are members of Congress who are skittish,” said Shawn Gremminger, senior director of federal relations for patient advocacy group Families USA. “They want to protect their [constituents], sure, but they are leery of something that is going to piss off one of the major industries in their state.”

Gremminger said he can envision the dispute causing lawmakers to throw up their arms and say the issue is too complicated to be fixed now, while offering vague promises to revisit it later.

One compromise solution can be found in the bill passed by the House Energy and Commerce Committee, which includes rate setting but also allows providers to appeal fees to an arbitration process.

Insurance companies are already involved in a lobbying blitz in favor of benchmarks and against arbitration. They argue arbitration would lead to higher costs and a bloated bureaucracy flooded with hundreds of thousands of arbitration claims.

Families USA is opposed to any price-setting process that takes into account what providers charge for their services, which Gremminger called “just phony numbers” that have no relation to actual costs or what the market could bear.

With Congress needing to pass a spending bill by the end of September to avoid a government shutdown, surprise billing could take a backseat. Staff from both parties say the momentum from July to tackle the issue has stalled and floor votes are unlikely before late fall at the earliest.

That means the lobbying and PR battle between insurers, hospitals, and doctors will continue to rage. Patient advocacy groups are planning a media campaign as well, though with fewer resources, it will be on a smaller scale than those paid for by the health industry groups. “It will not be in the millions, I’ll tell you that,” said Gremminger.