Medicare enrollees would have out-of-pocket drug costs capped at $7,500 under a bill introduced Sen. Ron Wyden, D-Ore., the top Democrat on the Senate Finance Committee.

Wyden cited 2013 data saying 2.9 million seniors enrolled in Medicare Part D paid above that threshold. Under the current law, beneficiaries have to pay 5 percent of additional drugs costs above $7,500.

“Escalating drug prices are increasingly straining the budgets of families in Oregon and across the country, particularly seniors in Medicare who often have to take multiple costly medications to stay healthy,” Wyden said in a statement. “It defies common sense that protection from high out-of-pocket costs exists for almost all other types of health coverage, but not for traditional Medicare.”

The legislation mirrors caps on out-of-pocket costs included in insurer plans sold on the Affordable Care Act’s marketplaces.

The bill would take effect in plan year 2018. However, it doesn’t specify a way to pay for the expected additional cost being shifted onto Medicare from enrollees. The legislation has also so far attracted Democratic co-sponsors: Sens. Ben Cardin, D-Md.; Maria Cantwell, D-Wash.; and Michael Bennet, D-Colo.

In a recent survey by AARP, 93 percent of respondents over the age of 50 supported allowing Medicare to negotiate for lower drug prices.