As the fate of Affordable Care Act subsidies lingers in a legislative limbo, U.S. Rep. Jake Auchincloss, D-Newton, is hoping to protect patients from a price surge on prescription drugs.

On Friday, Auchincloss introduced the ACA Copay Cost and Affordability for Patients (CAP) Act aimed at limiting annual prescription drug cost-sharing for people in ACA Marketplace health insurance plans.

“Insurance doesn’t work if the co-pays and deductibles are unaffordable,” Auchincloss wrote in a statement announcing the bill. “When people pay premiums to insurance companies, they should be able to trust that the insurer will cover them when a doctor prescribes a drug they need. My bill is a step towards repairing that trust.”

There are currently about 24 million Americans who get their health insurance through the Affordable Care Act Marketplace, the highest number in the program’s 15-year history.

Much of the division in Congress that led to the federal government being shut down recently related to Affordable Care Act subsidies, which help moderate-income Americans pay for health insurance plans they buy through the ACA exchange. Those subsidies are still at risk, and prescription drug prices—which ACA plans are required to offer at least some coverage for—are still rising.

Plans have maximum out-of-pocket costs for patients. And those limits are rising, too. A recent study by No Patient Left Behind reports that ACA patient prescription drug costs have gone up by an average of 36 percent since 2021. With many Americans having to pay thousands of dollars out-of-pocket before they hit their prescription cost-sharing limit, sharp spikes in drug prices can force families to choose between medicine and financial devastation.

Auchincloss’s bill would set new limits on out-of-pocket prescription costs and, starting in 2027, set a $2,000 annual cap on prescription drug costs for patients who get coverage individually and a $4,000 annual cap for family coverage.

And starting in 2028, the limit on prescription drug costs would increase every year based on a percentage determined by the secretary of Health and Human Services.

“Prescription drugs comprise just 10 cents of every dollar spent on health care. Yet from 2021 to 2023, insurers increased pharmacy copay costs for the average enrollee by 36%, and 5.6% of people had more than $2,000 in annual drug costs,” No Patient Left Behind Executive Director Peter Rubin said. “Patients and taxpayers expect premiums to pay for actual treatments. It is time to improve health plan quality. Thanks to Rep. Auchincloss and the ACA Copay CAP Act, we’re one step closer to real truth in insurance by requiring health plans and their vertically integrated PBMs to provide meaningful consumer protections from unaffordable out-of-pocket drug costs.”