FBI agents arrested several union members of Philadelphia’s Ironworkers Local 401 Wednesday on multiple counts including arson, violent crime in the aid of racketeering, and conspiracy under the Racketeer Influenced and Corrupt Organizations Act.

The investigation is ongoing and will likely scrutinize unions’ allies in political office, according to sources.

National Review wrote extensively about Ironworkers Local 401 last year as part of a broader investigation into how, for decades, organized labor has dominated the construction industry in Philadelphia through violence, intimidation, harassment and vandalism. Investigations and arrests have long been rare.

The 49-page indictment details how members of Local 401, who called themselves “the Helpful Union Guys,” or “THUGS,” allegedly extorted, intimidated and bullied businesses and contractors, forcing them to hire union members, even when they were “unwanted, unnecessary and superfluous.”

Members used arson, vandalism, sabotage and occasional violence to retaliate against those who chose to use non-union workers, the indictment says. Local 401 members were also allegedly behind the arson attack on a Quaker meeting house just days before Christmas 2012, which resulted in $500,000 in damage. The indictment also accuses two ironworkers of participating in a 2010 baseball-bat assault on non-union workers building a Toys R Us store in King of Prussia.

The indictment describes tense relations between unions, which became especially heated when Local 401 believed other workers were encroaching on ironwork jobs.

“You hope you get cancer so you can just go there and shoot every mother f*cker [member of the other union] down there,” said Ed Sweeny, a Local 401 business agent, according to the indictment. “You want to get cancer and just go there and shoot everybody. It’s insane, man, to have, to actually, to wish, you know, you would die so that you can go down there and kill them.”

Unions are almost never targeted as criminal organizations, in large part because in 1973 the Supreme Court ruled in United States v. Enmons that union officials cannot be prosecuted or even investigated if they are carrying out “legitimate union business.”

In the past, that’s often prevented unions from investigation under RICO or the Hobbs Act, which prohibits “the “wrongful use of actual or threatened force, violence, or fear,” and defines extortion as “the obtaining of property from another, with his consent . . . under color of official right.”

Edward Hanko, the FBI’s Special Agent in Charge in Philadelphia, tells National Review that though it was “a long and complex road,” he believes Enmons will not extend legal protections to the ironworkers indicted yesterday, many of whom could spend the rest of their lives in prison.

“Here’s where, of course, the difference comes: When you commit acts of violence, threats, intimidation, arson — that’s when you stop doing legitimate business for a union. That’s criminal activity. The difference is what allowed us to go forward with the RICO investigation,” Hanko explains.

In the past, many Philadelphia residents didn’t report criminal behavior from unions because they were afraid, Hanko says. “Maybe now that they can see a tangible result of a federal investigation, it will spur more people to come and tell their stories,” he says.

Rob Reeves Jr., the contractor building the Quaker meetinghouse that Local 401 allegedly vandalized, calls the indictment “a step in the right direction.”

“I hope it puts a chilling effect on other unions that have been doing very much the same type of thing for decades,” Reeves tells me. “It’s not just the Ironworkers. It’s the building trades [also], and many of the various unions have done [similar] things throughout the years .”

National Review’s investigation found that although 143 Philadelphia-based incidents of union violence had been documented in news reports between 1975 and 2009, arrests were mentioned only 38 times, and only eight convictions were noted.

The National Right to Work Committee, which counted those instances, estimates that for every union-related criminal incident that makes the papers, another 10 go unreported. By that count, Philadelphia has endured 45 incidents of union violence every year for almost four decades.

— Jillian Kay Melchior writes for National Review as a Thomas L. Rhodes Fellow for the Franklin Center. She is also a senior fellow for the Independent Women’s Forum.