A former United Auto Workers senior official on Friday became the fourth person charged in a US probe of an alleged scheme to raid funds meant for training auto workers.

Virdell King, who retired from the UAW in 2016, was charged with one count of conspiracy to violate the Labor Management Relations Act.

The 65-year-old was responsible for negotiating and administering collective bargaining agreements between the union and Fiat Chrysler's American subsidiary. He also took part in collective bargaining talks between the union and the car maker in 2011 and 2015.

King allegedly used a credit card tied to a worker's training center to pay for a variety of goods for herself and others at UAW -- including designer clothes and shoes, golf equipment and concert tickets.

Prosecutors have now publicly accused four people in the alleged scheme, and court documents indicate that at least four others at FCA US and UAW may be implicated.

Detroit's chief FBI agent said the group was involved in years of fraud and corruption.

An investigation underway makes it "far more likely that leaders in the labor union movement who illegally profit at the expense of their membership will be held to account," the FBI's David Gelios said in a statement.

Former FCA financial analyst Jerome Durden reached a plea deal, admitting that he and others concealed gifts and payments to UAW Vice President General Holiefield, who died in 2015, and other UAW officials, according to court filings.

A Detroit grand jury in July indicted former FCA US executive Alphons Iacobelli, who was in charge of negotiating and administering collective bargaining agreements, and Holiefield's widow Monica Morgan.

In all, officials said more than $4.5 million in worker training funds were diverted over a five-year period ending in 2014.