The Federal Trade Commission took action Friday against the three largest pharmacy benefit managers, accusing the companies of “engaging in anticompetitive and unfair rebating practices that have artificially inflated the list price of insulin drugs,

Insulin, used by millions of Americans, has taken center stage in the high-stakes battle over health care costs. Though prescribed for the past 100 years, only three companies supply insulin in the U.S. and much of that is higher-cost branded versions, despite the increasing availability of lower-price biologic options.

At issue is a report released by the FTC in July called: “Pharmacy Benefit Managers: The Powerful Middlemen Inflating Drug Costs and Squeezing Main Street Pharmacies.” Express Scripts claims in the lawsuit that the report “is seventy-four pages of unsupported innuendo” leveled against it and other PBMs.