American Protective League

The American Protective League was a World War I-era private organization that along with federal police like the Bureau of Investigation worked in support of the anti German Empire movement and against anti-war citizens and organizations.Formed by A.M. Briggs, a wealthy Chicago businessman, at its height of power the APL had 250,000 members in 600 cities. Officially condoned by the Attorney General, the APL support to the Bureau of Investigation, the precursor to the FBI.A private organization with no legal authority, APL members acted as vigilantes, allegedly violating the civil liberties of American citizens. The APL has been accused of having illegally detained citizens associated with progressive,  labor, and  pacifist movements.
See more at Wikipedia.org...