PROVIDENCE — A Coventry contractor who was indicted in an FBI undercover kickback scheme has agreed to plead guilty to a criminal charge and is likely to go to federal prison.

Gerald Diodati, a Seekonk resident, signed the agreement Monday and is scheduled to enter the plea July 31 before U.S. District Judge William E. Smith. Two weeks ago, one of Diodati’s codefendants, Harold L. Tillinghast Jr., pleaded guilty to a conspiracy charge and agreed to cooperate with the government.

In Diodati’s plea agreement, there is no mention of his cooperation with prosecutors.

The lone remaining defendant in the case is Nicholas Manocchio, of Cranston. He has pleaded not guilty to charges of conspiracy and aiding and abetting.

In November, Tillinghast, Manocchio and Diodati were indicted on charges that they participated in a kickback scheme involving Rising Sun Mills, a redevelopment project on Valley Street in the city’s Olneyville neighborhood.

Manocchio was Tillinghast’s boss at the Providence offices of the Laborers’ International Union of North America.

The investigation that led to the charges was launched seven years ago when the FBI opened a fictitious construction firm, Hemphill Construction, which was pursuing work in Rhode Island and elsewhere in Southern New England. The business was in a retail plaza on Atwood Avenue in Johnston near a Providence Journal news bureau.

A few months after setting up shop, an undercover agent posing as a principal owner of Hemphill Construction met with Tillinghast and Diodati. They allegedly reached a deal under which Diodati and others would make payments in excess of $1,000 to Tillinghast and Manocchio.

In April 2003, Tillinghast allegedly told Diodati and the undercover agent that he would try to get Hemphill Construction a demolition contract at Rising Sun Mills. The deal involved a $2,000 kickback to Tillinghast, the authorities said.

The kickback scheme also had a backdrop of organized crime activity, authorities say. Matthew L. Guglielmetti Jr., a capo regime in the Patriarca crime family, did construction work at Rising Mills and participated in some of the meetings at Hemphill’s office. He is now serving a long sentence in federal prison on drug charges.

Tillinghast is the son of the late Harold L. Tillinghast Sr. and a nephew of Gerald M. “Gerry” Tillinghast, two mobsters who were convicted of killing loan shark George Basmajian in the 1970s.

Two years ago, Gerry Tillinghast was released from prison and worked at Diodati’s firm, Rhode Island Construction Services, in Coventry.

bmalinow@projo.com