In the new ERISA report, the CRS analysts look at one Supreme Court ERISA case that involves retirement plans and a second case that relates to states' efforts to impose rules on pharmacy benefit managers.

The Backdrop: PBMs help employer plans, insurers and other payers manage prescription benefits programs.

Pharmaceutical manufacturers, pharmacies and some employers have argued that the big PBMs are now negotiating deals that increase their own revenue, rather than saving plans or patients money. The PBMs say the critics are angry about their successful efforts to squeeze other players' profit margins.

Arkansas, Oklahoma, Texas and other states have tried to set PBM rules that apply to PBMs serving self-funded plans, not just to state-regulated insurance companies.

Related: Supreme Court takes up PBM case: Does ERISA preempt states' efforts to regulate drug prices?

Many employers, and the ERISA Industry Committee, a group for parties interested in employers' self-insured benefit plans, say any PBM rules that affect self-insured plans should come from Congress, not the states, to preserve ERISA preemption.

The CRS report: "Some federal lawmakers have expressed support for enacting federal measures designed to regulate PBMs, including measures intended to make their practices," the CRS analysts write in the new ERISA report. "Should Congress decide to enact PBM-related legislation, questions may arise regarding the interplay between such state and federal provisions."

The analysts note that a PBM bill debated in the previous Congress would have required PBMs to provide reports for ERISA plans.

"This legislation would not have amended ERISA's preemption clause or expressly addressed the degree to which states may regulate a PBM's functions in service to ERISA plans," the analysts write. "Congress may choose, should lawmakers deem it appropriate, to explicitly address this issue in any future legislation."

The analysts have no official role in drafting legislation or determining what Congress will do, but the report could reflect the kinds of thoughts bill drafters in Washington are thinking.