They called themselves "the Helpful Union Guys" - "THUGS" for short - and woe awaited any contractor who dared cross them by hiring non-organized workers. For, federal authorities alleged Tuesday, this "goon squad" of members of Ironworkers Local 401 set fires, started riots, and took crowbars to the competition in an effort to protect union jobs. FBI agents arrested 10 of the union's leaders Tuesday morning, including longtime head Joseph Dougherty, in a racketeering conspiracy case that appeared to affirm long-standing business complaints over the tactics employed by Philadelphia unions.