Sen. Bernie Sanders (I-Vermont) is calling on federal investigators to open a probe into insurance companies that are denying coverage for contraception despite a federal mandate that contraception be free of cost to patients.

In a letter sent to the Government Accountability Office (GAO) on Monday, Sanders, the chair of the Senate Health, Education, Labor and Pensions (HELP) Committee, pointed out that a recent investigation by Vermont officials found that, between 2017 and 2021, health insurers in the state charged patients $1.5 million for contraception that should have been fully covered. This affected 9,000 patients who are now eligible to be compensated by the three insurance companies named in the investigation.

He further pointed to a 2022 investigation by Democrats in the House Oversight Committee that found that health insurers routinely exclude contraceptive products from coverage, requiring patients to pay out of pocket for such products or denying requests for exceptions for coverage, even when there are no other equivalent products on the market.

Under the Affordable Care Act, health insurers are required to cover contraception. But investigations have repeatedly found that, in practice, insurance companies skirt the rules to deny coverage, while federal regulators are often slow to update lists of medications and services covered by the Affordable Care Act when new products are introduced. Oftentimes, insurance companies will argue that they don’t have to cover newer contraception methods if they cover another version of it.

These denials can end up costing patients hundreds of dollars out of pocket, and it is seemingly a widespread issue. A 2022 KFF survey found that a quarter of women with private insurance say that they had to pay out of pocket for at least part of their contraceptive costs.

“The ACA has been federal law for 14 years and we continue to see plans deny coverage and ignore the federal mandate. It is completely unacceptable that plans consistently defy mandated coverage and that there is little enforcement or accountability,” Sanders wrote. His letter was first reported by The Washington Post.

He calls on the GAO to clarify whether or not agencies responsible for administering the Affordable Care Act are ensuring that insurance companies are being compliant with contraception costs. Other Democrats have similarly called on federal agencies to look into insurance companies’ practices when it comes to denying contraceptive coverage multiple times in recent years.

Sanders’s letter comes as Republicans are waging an attack on contraception as part of the GOP’s all-out war on reproductive rights. Earlier this month, Senate Republicans voted against advancing a bill that would protect contraception access at the federal level, with all but two Republicans voting “no.”

Meanwhile, Republicans across the country are seemingly laying the groundwork for restricting contraception access, using lies that contraception is akin to abortion; according to a Washington Post analysis earlier this month, Republicans have blocked Democratic legislation to protect contraception access in at least 17 states in the last two years. Most recently, Virginia Gov. Glenn Youngkin vetoed a bill passed by the Democratically-controlled state General Assembly that would have guaranteed the right to contraception access in the state.