A new Democratic bill would prevent Medicare Advantage (MA) plans from dropping providers in the middle of the year.
The measure is forthcoming from Rep. Rosa DeLauro (D-Conn.) and responds to UnitedHealth's move to drop thousands of doctors from its MA policies at the end of last year.
"Congress has to hold these companies accountable, and make sure they are putting the care of their enrollees ahead of their profits."
Fights over Medicare Advantage are especially hot this year given the issue's relevance in the midterm elections.
Last week, the Obama administration chose to reverse a proposed cut to the program after Republicans indicated they would use the reduction to target vulnerable Democrats.
Medicare Advantage, a privately run alternative to traditional Medicare, is paid more on average per beneficiary by the government.
Democrats and the Obama administration support paring back the program's reimbursements in order to make them more equal with those of regular Medicare.
Republicans and insurers argue the cuts would harm patients and take away popular benefits.
In December, UnitedHealth blamed its decision to narrow MA plan provider networks on "an era of Medicare Advantage funding cuts."
DeLauro's bill, the Medicare Advantage Participant Bill of Rights Act, would require MA plans to finalize their provider lists 60 days before the annual enrollment period.
It would also prohibit the plans from dropping providers in the middle of the year, when policyholders cannot choose new coverage.