The Illinois attorney general's office says a subpoena has been issued in the investigation into Volkswagen.
Attorney General Lisa Madigan's spokeswoman Eileen Boyce didn't have other details Wednesday, including what had been requested or the scope of the probe.
More than two dozen attorneys general, including Madigan, launched an investigation last week after the German automaker admitted it rigged diesel emissions technology to pass U.S. smog tests.
The state attorneys general said then that they anticipated sending subpoenas.
Participating states include Alabama, Arizona, California, Connecticut, Delaware, Florida, Illinois, Indiana, Iowa, Kentucky, Maine, Maryland, Michigan, Mississippi, Nebraska, Nevada, New Mexico, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Rhode Island, Tennessee, Texas, Vermont and Virginia, plus Washington, D.C.
A U.S.-based Volkswagen spokeswoman didn't immediately return messages from The Associated Press on Wednesday.