Federal agents reportedly raided the home of the United Auto Workers (UAW) President Gary Jones and the home of the union's former President Dennis Williams.
Sources told The Detroit News about the raids, which are part of the expansion of a corruption probe into auto industry attempts to affect union negotiations.
According to the newspaper, nine people had previously been charged and eight have been sentenced to prison in the investigation.
Agents reportedly served multiple search warrants including at Jones's Canton, Mich., home, Williams's California home and at the UAW Black Lake Conference Center, The Detroit News reported.
Mara Schneider, a spokeswoman for the FBI's Detroit branch, confirmed in a statement to The Hill on Wednesday that the agency searched a residence in Canton and a location in Black Lake, Mich., but said she could not confirm who they belonged to.
She also said she could not comment on the nature of the investigation.
The UAW issued a statement on Wednesday saying there was "no need" for the search warrants.
"The UAW and President Gary Jones have always fully cooperated with the government investigators in this matter," the statement said. "The UAW has voluntarily responded to every request the government has made throughout the course of its investigation, produced literally hundreds of thousands of documents and other materials to the government, and most importantly, when wrongdoing has been discovered, we have taken strong action to address it."
The union added that it will continue to cooperate with the investigation and said Jones is "determined to uncover and address any and all wrongdoing."
According to The Detroit News, the searches are occurring amid contract negotiations between the UAW and automakers. Experts told the paper the talks could be affected.