CVS Health, Cigna and UnitedHealth Group sued the Federal Trade Commission on Tuesday, alleging that the administrative process the Lina Khan-led agency is using to prosecute claims that their pharmacy benefit manager subsidiaries artificially inflated insulin prices violates their constitutional rights.

Rhode Island-based CVS owns Caremark Rx, Connecticut-based Cigna owns Express Scripts and Minnesota-based UnitedHealth owns OptumRx, the nation's three largest pharmacy benefit managers. PBMs act as behind-the-scenes middlemen, negotiating discounts with drug manufacturers and reimbursement rates with insurers and determining which medications qualify for coverage.