N.Y. AG Andrew Cuomo. Source: www.nndb.com

New York Attorney General Andrew Cuomo's office has issued subpoenas to eight health insurance company CEOs, including UnitedHealth Group's Stephen Hemsley, in an expansion of Cuomo's investigation into reimbursement practices of health insurers.

Cuomo had originally planned to sue UnitedHealth Group and its subsidiary Ingenix, calling the insurer part of an industry-wide effort to defraud consumers by manipulating reimbursement rates.

In February, Cuomo's office issued 16 subpoenas to health insurance companies including Aetna, Cigna and Empire BlueCross BlueShield as part of a six-month investigation into how the insurance industry handles reimbursements for physicians who are outside of a health plan's network.

A representative from Cuomo’s office told Bloomberg News that it has issued another 20 subpoenas that included demands for depositions of CEOs from insurers, including those at Cigna, Aetna and WellPoint.

UnitedHealth has refused to confirm or deny the subpoenas.