A federal corruption investigation targeting United Auto Workers leaders has ensnared its highest-ranking official yet: an ex-union president charged with stealing union funds to pay for private villas, expensive cigars, golf outings and other luxuries.

Federal prosecutors accused Gary Jones, the former head of the 400,000-member union, of conspiring with other senior UAW officials to embezzle more than $1 million and covering up the alleged misconduct with fake receipts and fraudulent expense reports, according to charging documents filed with a Michigan federal court and made public Thursday.

The 63-year-old Mr. Jones, who was named president in 2018, most recently led the UAW through contract talks with the Detroit car makers last fall and a 40-day strike at General Motors Co.

The charges are the latest escalation in the government’s probe and come as the 84-year-old union is struggling to reverse membership declines and win back the trust of rank-and-file workers, whose confidence in senior leadership has been dented by the expanding federal investigation.

Prosecutors say the alleged misconduct, spanning from 2010 to last September, was part of a racketeering scheme that violated federal laws.