Last week, Senator Bernie Sanders of Vermont, chair of the Senate health committee, called on a government watchdog to investigate why insurance companies are still charging women for birth control — a move that thrust access to contraceptives back into the spotlight.

In a letter to the Government Accountability Office, the senator noted that insurance companies were charging Americans for contraceptives that, under federal law, should be free — and that they were also denying appeals from consumers who were seeking to have their contraceptives covered. Some experts estimate that those practices could affect access to birth control for millions of women.

Since 2012, the Affordable Care Act has mandated that private insurance plans cover the “full range” of contraceptives for women approved by the Food and Drug Administration, including female sterilizations, emergency contraceptives and any new products cleared by the F.D.A. The mandate also covers services associated with contraceptives, like counseling, insertions or removals and follow-up care.

That means that consumers shouldn’t have any associated co-payments with in-network providers, even if they haven’t met their deductibles. Some plans might cover only generic versions of certain contraceptives, but patients are still entitled to coverage of a specific product that their providers deem medically necessary. Medicaid plans have a similar provision; the only exception to the mandate are plans sponsored by employers or colleges that have religious or moral objections.

Yet many insurers are still charging for contraceptives — some in the form of co-payments, others by denying coverage altogether.

A Quarter of Women Are Paying Unnecessarily for Contraceptives

In his letter, Senator Sanders cited a recent survey by KFF, a nonprofit health policy research organization, that found that roughly 25 percent of women with private insurance plans said they had paid at least some part of the cost of their birth control; 16 percent reported that their insurance plans had offered partial coverage, and 6 percent noted that their plans did not cover contraceptives at all. Additionally, a 2022 congressional investigation, which analyzed 68 health plans, found that the process to apply for exceptions and have contraceptives covered was “burdensome” for consumers and that insurance companies denied, on average, at least 40 percent of exception requests.

In a letter responding to Congress earlier this year, AHIP, a national lobbying group that represents insurance companies, noted that the group “will continue to partner with the Administration, Congress, and policymakers to ensure that consumers have affordable access to contraception consistent with the law.”

Despite the fact that the federal mandate has existed for more than a decade, companies continue to skirt the law because “these mandates are rarely enforced, and the penalties for ignoring them are relatively low,” said Anna Bahr, director of communications for Senator Sanders. Each time a company is penalized, it finds other ways to deny coverage, she said.

In 2015, a study by the National Women’s Law Center, a nonprofit legal organization, found that several insurance companies claimed they were not covering hormonal rings, intrauterine devices or patches because they covered another hormonal method: the birth control pill. That practice was a violation of the mandate and prompted the Obama administration to crack down.

Today, the complaints from consumers are slightly different, said Gretchen Borchelt, vice president of reproductive rights and health at the law center. The group has heard from women whose plans have a “try and fail” caveat, in which patients are expected to try specific products, usually oral contraceptive pills, until those “fail,” before they can get the contraceptive option they want and that their provider recommends for them.

Earlier this year, the Department of Labor, which is one of the three government agencies responsible for enforcing the Affordable Care Act mandate, called that practice “problematic.”

Insurance companies also frequently deny coverage for newer F.D.A.-approved contraceptives, said Alina Salganicoff, senior vice president and director for women’s health policy at KFF. The organization also found that companies might cover a birth control product, like an I.U.D., but deny coverage of the associated services, like insertion or removal, she said. According to a study published last summer, the portion of privately insured women who had paid nothing for their I.U.D.s or implants has been declining since 2015.

What to Do if You Are Charged for Contraception

Talk to both your doctor and your insurance company and remind them that the law says you shouldn’t have to pay, Ms. Salganicoff said.

You can also call the National Women’s Law Center hotline, which will help you take a thorough look at your plan to figure out what the problem is, Ms. Borchelt said. Sometimes the hotline is able to help patients obtain reimbursements.

Consumers should also let their representatives know, she said, because complaints like these can often be investigated.

Complaints from consumers in Vermont prompted a two-year investigation into health insurance plans there that found that nearly 9,000 people had been wrongly charged for contraceptives. As a result, the state ordered insurance providers to issue $1.5 million in reimbursements last year.

“Public pressure helps a lot,” Ms. Borchelt said.