Three more members of Ironworkers Local 401 in Philadelphia pleaded guilty Tuesday to charges of conspiracy, extortion, and racketeering in an ongoing RICO case against the labor union. They join eight others who have pleaded guilty in recent months to charges related to arson, sabotage, and violent intimidation of contractors who used non-union labor.

Ironworkers 401 is a large and influential union, responsible for constructing many of Philadelphia’s landmarks, such as Lincoln Financial Field, the Eagle’s football stadium, and the Comcast Center, the city’s tallest building. But this year has brought a series of indictments and revelations that continue to produce serious fallout for the labor group and its allies.

The latest hit came on Tuesday, when union member Richard Ritchie and business agents William O’Donnell and Christopher Prophet entered plea agreements admitting to their role in a conspiracy to coerce non-union construction sites into using “unwanted, unnecessary, and superfluous union labor.”

According to a statement from the U.S. Attorney’s Office, Prophet also pleaded to attempted extortion and Ritchie to attempted extortion and violent crime in aid of racketeering. In February, over 100 federal agents and police descended on Ironworkers Local 401, one of the biggest and most powerful unions in the Philadelphia area, sweeping up officials and members alleged to be part of the conspiracy. The federal indictment spans over 60 pages, alleging a coordinated effort by a network of union associates to locate and identify construction projects that used non-union workers (or the rival carpenters’ union) to do “ironwork.”

The union’s business agents would visit foremen and threaten them with assault and sabotage if they did not agree to hire 401 members, prosecutors claim, although often such workers “often performed little or no actual work” and were paid “merely to prevent further acts of sabotage.” If the foreman did not concede, union members would use a series of tactics, from picketing to physically barring workers and materials from entering the site, to increase the pressure. If this did not work, things would escalate to violence and vandalism: “actions included assaulting non-union employees with baseball bats, slashing the tires of vehicles, smashing vehicles with crow bars, cutting and changing the locks on construction sites, filling the locks with superglue, damaging construction equipment, [and] stealing construction materials.”

If the contractors still resisted, more severe sabotage – what members referred to as “night work” – is alleged to have followed, including setting fire to the site, destroying machinery, and “using an acetylene torch … to cut through the steel support columns of the building.”

In one case, defendants are said to have set fire to a crane at a Quaker meetinghouse that was using non-union workers. The indictment alleges that the union maintained teams of saboteurs it refers to as “goon squads” to perform this kind of criminal activity in exchange for preferential treatment on job assignments. One such group is supposed to have called itself “T.H.U.G.’s”, for “The Helpful Union Guys.”

All but one the 12 defendants charged in the case have pleaded guilty, receiving sentencing recommendations in exchange for their cooperation as witnesses against Joseph Dougherty, the 72-year-old head of the Local 401 and the alleged ringleader of the conspiracy. Such plea deals are not unusual in the federal system, and about 90 percent of criminal defendants prefer to take a plea bargain than risk the harsh sentences allowed and required under federal law. Without a favorable sentencing recommendation, Ritchie could face up to 60 years in prison, Prophet up to 40 years, and O’Donnell up to two decades.

Dougherty, however, has maintained his innocence throughout the indictment and intends to go to court. Jury selection for his case has been completed, and the trial is scheduled to begin on January 5, 2015, and will be prosecuted by Assistant U.S. Attorney Robert Livermore. Sentencing hearings for all of the defendants who have pleaded guilty are set to take place only after the conclusion of Dougherty’s trial.