In an emergency, people often don’t think about whether the ambulance company is in their insurer’s network. That’s one reason why ambulance riders are among the most likely to get slammed with surprise medical bills, according to a survey by Consumer Reports and the nonprofit group Consumers Union. Among more than 700 stories of surprise medical bills the groups collected, at least a quarter involved ambulance rides.

In some states, private insurance companies negotiate prices with ambulance services to keep their costs down. In other cases, a public health system runs the service and can regulate fees. But most states don’t, leaving patients on their own to try to figure out the best price for a ride. When ambulance and private insurance providers can’t agree, the provider may charge the patient out-of-network rates, a practice called balance billing. The Consumer Reports survey found that out-of-network charges on ambulance rides can cost patients hundreds or thousands of dollars.

A Texas lawmaker is trying to change that. Rep. Lloyd Doggett, a Democrat, has introduced legislation that would limit the ability of private ambulance companies to balance bill patients. “These companies are taking advantage of consumers and causing them to have unexpected and unaffordable medical bills,” he says. The bill would also require that state regulators investigate complaints about ambulance companies’ practices.

Many states have laws against surprise medical bills, but they don’t all cover ground ambulances. The exception is Medicare and Medicaid, which ban balance billing for patients on those government-sponsored programs. The two government-run health insurance programs also have lower reimbursement rates for ground ambulances, which puts them in a better position to negotiate.

Ambulance services also may charge different amounts for the same service, based on things such as whether it’s an emergency or non-emergency ride, or if the patient is in or out of their area. A recent study found that non-emergency rides by ground ambulances for people with private insurance can cost as much as $700 — which can be hard to pay.

When a couple from Roswell, Georgia, needed help for their 20-month-old daughter after she had a seizure, they knew to call 911. But a few months later, they still are fighting an AMR bill for the trip. That’s because AMR didn’t mention when they called that it might not be in-network.

If you have a complaint about an American Medical Response Billing, doxo is here to help. doxo is a secure, all-in-one app that lets you organize your bills and make payments to thousands of billers. It’s free to use if you pay with a bank account, and only $2 for other types of payments. Learn more.

We’ve got tips to help you avoid ambulance surprises. You can ask your insurer to review the claim and see if they’ll cover more of it. If a phone call doesn’t work, you can file a complaint with your state’s insurance department or attorney general. We’ve put together a handy guide with step-by-step directions, along with a sample letter from the Patient Advocate Foundation.