The Federal Trade Commission is launching an inquiry into the operations of pharmacy benefits managers that control access to prescription drugs for millions of Americans.

The consumer protection agency will order the nation’s largest PBMs to provide a range of information and records detailing how they do business. Pharmacy benefits managers run prescription drug coverage for big clients, including health insurers and employers that provide coverage to their employees. They help decide which drugs make a plan’s formulary and can also determine where patients go to fill their prescriptions.

These businesses — the biggest of which are run by companies that also operate health insurers — have been criticized by doctors and patients over their formularies and other concerns about drug access.

Read: PMPRB drug pricing regulations officially coming into effect this July

In a statement, FTC Chair Lina M. Khan said PBMs have “enormous influence” over the country’s prescription drug system. “This study will shine a light on these companies’ practices and their impact on pharmacies, payers, doctors and patients.”

The FTC said it will seek to learn more from PBMs about drug manufacturer rebates and how they affect formulary design and the cost of drugs. The agency will also look at “complicated and opaque methods to determine pharmacy reimbursement” and how patients are steered toward PBM-owned pharmacies.

The federal agency said the FTC Act authorizes it to conduct studies without a specific law enforcement purpose and companies will have 90 days from the date they receive an order to respond.

Read: Private drug plan spend increased 4.3% in 2021: report