New York CNN Business  — 

Federal agents searched the home of the president of the United Auto Workers union Wednesday as part of an ongoing probe of alleged corruption involving the union and at least one of the nation’s unionized automakers.

The years-long probe has already led to charges against nine people with ties to the union and Fiat Chrysler. Eight of those charged have pled guilty and been sentenced; charges are pending against the ninth.

Agents of the FBI searched the suburban Detroit home of UAW President Gary Jones as well as UAW Black Lake Conference Center, a retreat on 1,000 heavily-wooded acres on the shore of a northern Michigan lake, and locations in at least three other states, an FBI spokesperson confirmed to CNN.

She said the agents arrived at 7:30 a.m. and were finished by early afternoon, declining to comment on the nature of the evidence recovered. Agents from the IRS and the Labor Department were also present for the search.

The union issued a statement saying it is cooperating with the probe and that the use of search warrants was unnecessary.

“The UAW and President Gary Jones have always fully cooperated with the government investigators in this matter,” the statement said. “President Jones is determined to uncover and address any and all wrongdoing, wherever it might lead. 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.”

UAW Vice President Norwood Jewell, who once headed negotiations with Fiat Chrysler, pleaded guilty in April to accepting, arranging and approving illegal payments from Fiat Chrysler executives to high-level union officials. Fiat Chrysler Vice President for Employee Relations Alphons Iacobelli also pleaded guilty in the conspiracy, as did six others.

The investigation comes as the union’s contract negotiations with the three unionized automakers — General Motors (GM), Ford (F) and Fiat Chrysler (FCAU) — are ramping up. The contracts with all three automakers are due to expire Sept. 15, although the contracts could be extended depending upon progress at the bargaining table.

But this time negotiations are seen as very difficult.

The automakers have suffered from declining sales and the need to invest heavily in the next generation of electric and self-driving cars. GM is in the process of closing four of its 30 US plants as part of a $4.5 billion cost-cutting effort. Ford recently cut 7,000 white collar jobs and says it will spend $11 billion reshaping the company.

The union, however, is not interested in granting cost-saving concessions to the three companies, which in 2018 had combined net profits of nearly $16 billion.

In negotiations four years ago, rank-and-file UAW members narrowly approved contracts agreed to by union leadership, despite the deals containing the first wage increases in a decade. This time, if rank and file members lose confidence in union leadership, they might be less inclined to ratify whatever deals are struck at the bargaining table.