New York state attorney general Eric Schneiderman has issued subpoenas to 16 health insurance companies demanding documents to explain how they decide who should be included in treatment for hepatitis C. According to a person involved with the investigation, some insurers are restricting coverage of treatment because of costly medication.

The hepatitis C medications, made by Gilead Sciences Inc. and AbbVie Inc., have been in controversies for their high price. The drugs can cure a patient in just 12 weeks. A pill costs about $1,000, while full treatment can be accounted for about $84,000.

Insurers play their role in negotiating the discounts with the manufacturers. However, some insurers do not have sufficient access to the drugs, which restrict them from responding to demands of sickest patients for treatment, who generally can’t afford medication.

The insurers include Anthem Inc., Aetna Inc. and Emblem Health Inc. Anthem operates the Empire Blue Cross Blue Shield insurance company quoted that it has expanded coverage of the hepatitis drugs recently.

“After several months of ongoing clinical review of the medical evidence and safety concerns surrounding hepatitis C treatments, coverage for Empire Blue Cross Blue Shield employer and individual health insurance plans was expanded for six of the newer oral treatments effective Dec. 7, 2015,” said Anthem spokeswoman Jill Becher.

A study by Trio Health, a disease management firm, found that Medicaid refused to give prescription to at least 30% of patients in more than 2,000 patients between October 2014 and March 2015. Medicaid is a US health program for poor and disabled people. While, at least 14% of patients couldn’t start treatment when covered by commercial insurers.