For five years, federal investigators have pieced together a broad pattern of corruption within the United Automobile Workers. They documented the diversion of dues for high living by union officials and found a conspiracy that may have compromised dealings with a leading automaker.

Now prosecutors have taken aim at their biggest target yet, charging a former U.A.W. president with embezzlement of union funds. And they left no doubt that there may be more to come — possibly including a federal takeover of the union, a pillar of the nation’s labor movement.

In a criminal filing unsealed Thursday, the former president, Gary Jones, is accused of misusing more than $1 million of union money for extravagant meals, golf outings, cigars, apparel and other purposes over several years before his election in 2018.

He is the highest-ranking U.A.W. official to be prosecuted in the inquiry, in which more than a dozen people have pleaded guilty, including several former union officers and three former Fiat Chrysler executives. One of those executives, the company’s chief labor negotiator, was found to have used funds from a training program for union workers to buy a Ferrari and renovate his home.