By Around 1903, employers began to mount organized campaigns to break the power of labor unions, particularly in the metal trades. Employers had a broad array of weapons in their arsenal, including blacklists, strikebreakers, and court injunctions against strikers' use of boycotts and sympathy strikes. Although early twentieth-century employers had reliable allies in state police forces and tightly controlled local police, they continued to hire their own private police—detective agencies that used secret operatives to disrupt unions and supplied thugs to protect strikebreakers during strikes. This 1917 ad for the Cleveland-based Joy Detective Agency appeared in American Industries, the official publication of the National Association of Manufacturers.
We break strikes—also handle labor troubles in all their phases. We are prepared to place secret operatives who are skilled mechanics in any shop, mill or factory, to discover whether organization is being done, material wasted or stolen, negligence on the part of employees, etc., etc. . . . We guard property during strikes, employ non-union men to fill places of strikers, fit up and maintain boarding houses for them, etc. Branches in all parts of the country; write us for references and terms. The Joy Detective Agency, Cleveland, Ohio, Incorporated.
Source: American Industries, 15 April 1907. Reprinted in Harry W. Laidler, Boycotts and the Labor Struggle (New York: John Lane Company, 1913), 293–294.