FILE PHOTO: Fiat Chrysler Automobiles' (FCA) U.S. headquarters is seen in Auburn Hills, Michigan, U.S., May 25, 2018. REUTERS/Rebecca Cook/File Photo

DETROIT (Reuters) - Top officials of Fiat Chrysler Automobiles NV and the United Auto Workers (UAW) union conspired to violate U.S. labor laws, federal prosecutors alleged in a court document, saying a former executive at the automaker knew bribes paid to union leaders were designed to “grease the skids” in labor negotiations.

U.S. Justice department officials called the company and the union “co-conspirators” in a document related to a guilty plea agreed by former Fiat Chrysler director of employee relations Michael Brown. The document was filed with the U.S. District Court in Detroit on May 25. Its contents were reported by the Detroit News on Wednesday.

Brown pleaded guilty to one count of concealing a felony. The plea agreement stated that he knew Fiat Chrysler executives authorized improper payments and paid for travel, liquor, cigars and other goods for UAW officials who served on the union’s negotiating committee.

Fiat Chrysler Chief Executive Officer Sergio Marchionne has said in the past that the misconduct had “had nothing whatsoever to do with the collective bargaining process” and the “egregious acts were neither known to nor sanctioned” by the company. Fiat Chrysler had no further comment Monday.

Outgoing UAW president Dennis Williams told union leaders at a conference in Detroit on Monday “our leadership team had no knowledge of the misconduct – which involved former union members and former auto executives – until it was brought to our attention by the government.”

Brown pleaded guilty on May 25, according to court documents, and will be sentenced on Sept. 20. Five other people have pleaded guilty in the government’s ongoing investigation into the UAW and Fiat Chrysler, including the wife of a late UAW official, two other former UAW employees, former Fiat Chrysler vice president Alphons Iacobelli and another former Fiat Chrysler employee.