Issa, chairman of the House Oversight and Government Reform Committee, sent letters Monday to the chief executive officers of 15 U.S. automakers, including Ford, Chrysler and General Motors, seeking information on the negotiations, The Hill reported Tuesday.
The talks resulted in stricter fuel-economy standards for cars and trucks.
"I am concerned about the agreements lack of transparency, the failure to conduct an open rulemaking process, as well as the potential for vehicle cost increases on consumers, and negative impact on American jobs," Issa wrote to automakers in July at the start of the investigation.
Issa also has requested information on fuel-economy standards from the Environmental Protection Agency and the Department of Transportation, The Hill said.
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