The federal investigation into the U.A.W. began more than five years ago and is still active. Among those still under scrutiny is Mr. Jones’s predecessor, Dennis Williams. A plea agreement in February with a former aide to Mr. Jones indicated that a U.A.W. officer, whom court filings refer to as Official B, had urged using union money in ways that would benefit himself and other officials. Union officials have confirmed that Official B is Mr. Williams. The union also built a luxurious lakeside cabin for Mr. Williams at a U.A.W. resort about 250 miles north of Detroit.
A lawyer for Mr. Williams did not respond to requests for comment.
The U.S. attorney in Detroit, Matthew Schneider, has previously said that he could not rule out a federal takeover of the U.A.W. Another union that was the subject of a corruption investigation, the International Brotherhood of Teamsters, regained its independence in February after 30 years of federal oversight.
The investigation has dealt a big blow to the U.A.W. Mr. Gamble has apologized for its failings and has pledged to reform it. While the union no longer has the power and political influence it wielded decades ago, it remains one of the largest labor groups in the country and is a key player in the U.S. auto industry. The U.A.W. represents about 400,000 workers and is the biggest union at G.M., Ford Motor and Fiat Chrysler.
Mr. Jones pleaded guilty to two counts: for improperly using union funds and tax fraud for not reporting and paying taxes on that illicit income.
His plea agreement is the first time in decades that a union president of national stature has faced such serious criminal charges, said an expert on union corruption, David Witwer of Pennsylvania State University at Harrisburg. Professor Witwer pointed to the 1981 indictment of Roy L. Williams, president of the International Brotherhood of Teamsters at the time, on charges that he had conspired to bribe a senator in hopes of blocking or delaying a trucking deregulation measure.
Three years earlier, Joseph P. Tonelli, at the time the president of the United Paperworkers International Union and a top official with the A.F.L.-C.I.O., was charged along with other union officials for embezzling $360,000 from the union. Both leaders were later convicted.
The plea agreement marks a dramatic fall for Mr. Jones, who joined the U.A.W. as a welder and was elected president in 2018. Last year, he led workers through a 40-day strike against G.M. The strike yielded increased pay and benefits for temporary workers and those with less seniority, a key union goal. In exchange, the union accepted G.M.’s decision to close a plant in Lordstown, Ohio, a move that frustrated some U.A.W. members.