Chesapeake Energy Corp. (NYSE: CHK) said it received a subpoena from the U.S. Department of Justice (DOJ) seeking information on the accounting methodology for the acquisition and classification of oil and gas properties.

Shares of the company fell as much as 9.3% in morning trading.

The No. 2 U.S. natural gas producer said in May that it had received subpoenas and demands for documents from the DoJ and some state government agencies in connection with investigations into possible violations of antitrust laws relating to the purchase and lease of oil and natural gas rights.

Chesapeake had also received subpoenas from the DoJ, the U.S. Postal Service and states, seeking information on how the company pays royalties to landowners.

The company said in a regulatory filing on Sept. 29 that it had engaged in discussions with the DoJ, the U.S. Postal Service and state agency representatives and continues to respond to such subpoenas and demands.

Chesapeake had come under scrutiny when former CEO Aubrey McClendon, who helped transform the U.S. energy industry with shale gas, was investigated and charged in March with conspiring to rig bids to buy oil and natural gas leases in Oklahoma.

McClendon died one day later when his car slammed into an overpass.

Reuters reported in 2012 that McClendon had taken out more than $1 billion in loans using his personal stakes in thousands of company wells as collateral.

Chesapeake shares were down 4.2% at $6.46 on Sept. 29. Up to Sept. 28's close, they had risen 50% in 2016.