Sweeney described his role in such situations - he has also merged unions and taken over a North Jersey local accused of embezzlement - as "the cleanup."
"I go in when things like this happen, I fire people. I reorganize. And I try to restore the reputation of the union. This is not going to be easy because of what happened," he said.
Prosecutors allege that union officials used violence, and urged members to threaten and destroy the property of contractors who hired nonunion workers. The officials called themselves "the Helpful Union Guys," or THUGS, according to prosecutors.
Several of the indicted ironworkers, including business agent Ed Sweeney (no relation), were arraigned Thursday in federal court. Ed Sweeney declined to comment, as did his attorney, Carmen C. Nasuti.
"There's a thousand ironworkers over there, men and women: They're not thugs," Stephen Sweeney said. "You had some behavior - they're allegations - if they are true, it's personally, personally, devastating to me."
"This is horrible for the image of labor and, more importantly for me, ironworkers," he said.
Since 2000, Local 401 has donated a combined $10,500, a relatively small amount, to Sweeney and two affiliated groups: the Gloucester County Executive Committee (Sweeney was the county's longtime freeholder director) and a Senate Majority Leadership committee.
In the Senate, Sweeney has pushed for labor-friendly causes such as raising the minimum wage, though he also spearheaded a successful effort with Gov. Christie in 2011 to require public workers to contribute more toward their pensions, to the chagrin of the state's unions.
In his budget address this week, Christie, a Republican, intimated that public employees may need to contribute more to shore up the state's finances. Sweeney and other Democrats say the workers have already paid their fair share.
As for the Philadelphia local, Sweeney said: "I'm in the process of hiring new people. Then you have to train people. Then work three times as hard to let everyone know that the people we work with aren't about what allegedly had happened - that we don't support that."
Inquirer staff writer Jeremy Roebuck contributed to this article.