Following the Civil War, the Pinkertons began conducting operations against organized labor.[5] During the labor strikes of the late 19th and early 20th centuries, businesses hired the Pinkerton Agency to infiltrate unions, supply guards, keep strikers and suspected unionists out of factories, and recruit goon squads to intimidate workers.[6] During the Homestead Strike of 1892, Pinkerton agents were called in to reinforce the strikebreaking measures of industrialist Henry Clay Frick, who was acting on behalf of Andrew Carnegie, the head of Carnegie Steel.[7]