The U.S. Federal Trade Commission sued the country’s three largest pharmacy benefit managers on Friday, accusing them of steering diabetes patients towards higher priced insulin in order to reap millions of dollars in rebates from pharmaceutical companies.

The case accuses UnitedHealth Group Inc’s Optum unit, CVS Health Corp’s CVS Caremark and Cigna Corp’s Express Scripts of unfairly excluding lower cost insulin products from lists of drugs covered by insurers.

The conduct hurt patients, such as those with coinsurance and deductibles, who were not eligible for the rebated price, the FTC said. The three PBMs together administer 80% of all prescriptions in the U.S., according to the case, which was filed in the FTC’s in-house court.