A patient can do everything right and still face substantial surprise medical bills.

In his recent Oval Office speech, President Trump pledged that Americans won’t receive surprise bills for their coronavirus testing.

The goal is good; we need people who are lightly symptomatic to be tested without fear of high personal costs. But it was an empty promise. Unless swift action is taken, surprise bills are coming. And they could exacerbate a public health crisis that is already threatening to spiral out of control.

As demand for coronavirus testing surges and beds start to fill with the sick, hospitals and clinics will roll out contingency plans that call on any available resources in their communities. Test samples will be sent to whichever private laboratories have capacity, patients will be transferred from overloaded hospitals to less-crowded locations and physicians and nurses will make greater use of telemedicine.

Emergency rooms will be slammed with visits from the worried well and the dangerously sick alike. College students are already being sent home and will seek treatment far from the universities that offer them health insurance.

All of this will be chaotic.

To their credit, health insurers recognize the need to eliminate out-of-pocket spending that might discourage people from seeking care. At a meeting earlier this week with Vice President Mike Pence, they publicly committed to eliminating deductibles and co-pays for coronavirus testing. The federal government is also taking some needed steps to eliminate or ease cost-sharing.

But insurance companies aren’t the ones sending surprise bills. They’re coming from private labs and emergency-room doctors and other providers of health care services — and they weren’t at Vice President Pence’s meeting.

A patient with insurance through work or the health-insurance exchanges can be surprise-billed when she seeks medical care at a hospital or clinic that’s in her insurance “network” — but then receives medical care from a person or an institution that’s outside the network.

That out-of-network provider will first send a bill to the patient’s insurer. But if the insurer doesn’t pay the full amount, the provider may bill the patient directly for the remaining balance. Because the provider is basically free to name its own price, these surprise bills can be wildly inflated.

In a coronavirus pandemic, a patient can do everything right and still face substantial surprise bills. Take someone who fears that she may have contracted Covid-19. After self-quarantining for a week, she develops severe shortness of breath. Her partner rushes her to the nearest in-network emergency room. But she’s actually seen by an out-of-network doctor — who may soon send her a hefty bill for the visit.

Matters get worse if the in-network hospital is approaching capacity and the patient is healthy enough to be sent to a hospital across town with spare beds. If the second hospital is outside her insurance network, she could potentially receive a second surprise bill. A third could come from the ambulance that transfers her — it too might not be in-network, and no one will think to check during a crisis. She could get a fourth surprise bill if her coronavirus tests are sent to an out-of-network lab. And so on.

Even in normal times, patients with private insurance receive roughly one surprise bill for every 10 inpatient hospital admissions.

These are not normal times.

Federal law currently provides little protection. The Affordable Care Act does cap an individual’s out-of-pocket spending — but the cap only applies to in-network care. For surprise bills, the sky is the limit.

Reputable providers will appreciate that now is not the time for price gouging. But many won’t and will seek to exploit people’s medical needs for financial gain, much as they did before the coronavirus began to spread. They may calculate that can collect enough money charging exorbitant fees for out-of-network services — and still make it to an airport ahead of a mob carrying pitchforks and torches.

We need more than gauzy commitments from the president. We need a law to ban bills incurred from out-of-network providers for medical care associated with the coronavirus outbreak. Unless that commitment is ironclad, people may not believe it. And if they don’t believe it, they won’t get tested.

To date, Congress — cowed by a furious public relations campaign led by private equity and specialty physicians — has been unable to pass a law banning routine surprise billing. Though Congress has moved closer to a watered-down deal in recent months, neither the House nor the Senate has actually passed a bill.

The coronavirus should refocus Congress’s attention. At a minimum, the legislature should quickly pass a temporary measure to limit out-of-network charges for coronavirus testing and treatment.

In the meantime, states can take action. About half have already passed surprise-billing laws, including California and New York, two of the hardest-hit states. But the laws in many states are patchy: Some cover only emergency room care, others don’t contain a legal mechanism for cutting back on excessive bills, and none are tailored for the current outbreak.

Already, reports of people who have received eye-popping bills for coronavirus testing or emergency room visits are circulating. As these stories proliferate, people will become even more reluctant to get tested or treated when they should. That will obscure the spread of the virus, complicate efforts to adopt measures for social distancing, and lead to unnecessary deaths.

It’s a national disgrace that the United States didn’t ban surprise bills in a time of relative prosperity and security. It could become a public health calamity if we do not end them in a world with coronavirus.