industrial union, labor union composed of all the workers in a given industry, regardless of skill, craft, or occupation (as opposed to the craft union, in which all members are of one skill, such as carpenters or electricians). The industrial union is sometimes referred to as a vertical union, since it accepts workers from the least to the most skilled as members. Prior to the 1870s, unions in the United States had been organized on a craft basis; a modified form of industrial union appeared with the Knights of Labor. The successor to that organization, the American Federation of Labor (AFL), organized new members on the basis of their craft. But the idea of an industrial union survived with the Industrial Workers of the World, which was founded in 1905. Adopting a policy of accepting everyone, skilled or unskilled and regardless of race, sex, or creed, the IWW's membership ranged from mine workers, to even migrant agricultural workers. Within the AFL in the 1930s one segment of unions, under the leadership of John L. Lewis, began to organize in the mass production industries, i.e., to form industrial unions. These unions, initially named the Committee for Industrial Organization, were expelled (1936) and were renamed (1938) the Congress of Industrial Organizations (CIO). The newly formed CIO was basically an industrial union. Three kinds of industrial unions were recognized—those consisting of all employees working on the same commodity (e.g., electrical workers or brewery workers), those using the same tools to work on different materials (e.g., textile and aluminum workers), and all employees of a given factory regardless of their particular skill. Following the merger of the AFL with the CIO in 1955, an Industrial Union Department (IUD) was organized within the merged organization. Although industrial unions have traditionally attempted to organize manufacturing or mining employees, such unions as the Service Employees International Union are now attempting to organize workers in service industries and the public sector. But organizing office workers who perform different tasks in various offices in separate buildings has been much harder than organizing a large automobile factory where all employees work on the same assembly line. See bibliography under American Federation of Labor and Congress of Industrial Organizations.