The mining companies controlled Bisbee, not only because they were the primary employers but because local businesses depended heavily on the mines and miners to survive. Even the local newspaper was owned by one of the major mining companies, Phelps Dodge.
Prior to 1917, union activity had repeatedly been stifled. Between 1906 and 1907, for example, about 1,200 men were fired for for supporting a union. Conversely, the Bisbee Industrial Association, an alliance that was pro-company and anti-union, was easily organized around the same time. Finally, in 1916, the International Union of Mine, Mill and Smelter (formerly the Western Federation of Miners) successfully enrolled 1,800 miners.
The Industrial Workers of the World's (I.W.W.) presence in Arizona was also increasing. Founded in 1905, the I.W.W. never recruited more than five percent of the trade unionists in the country, but many others were exposed to its ideas. Some of the I.W.W.'s tactics, such as advocating slowdowns and sabotage, were of great concern to the controlling interests. In addition, the I.W.W. adopted two successful recruiting practices. They actively recruited miners from minority groups. As a result, the IWW was particularly successful recruiting Bisbee's Mexican workers, who were routinely given lower paying jobs outside of the mine. The I.W.W. was also successful recruiting southern European immigrants, who were allowed in the mines but given lower paying jobs.
On June 24, 1917, the I.W.W. presented the Bisbee mining companies with a list of demands. These demands included improvements to safety and working conditions, such as requiring two men on each machine and an end to blasting in the mines during shifts. Demands were also made to end discrimination against members of labor organizations and the unequal treatment of foreign and minority workers. Furthermore, the unions wanted a flat wage system to replace sliding scales tied to the market price of copper. The copper companies refused all I.W.W. demands, using the war effort as justification. As a result, a strike was called, and by June 27 roughly half of the Bisbee work force was on strike.
Tensions heightened when rumors spread asserting that the unions had been infiltrated by pro-Germans. Another rumor suggested that weapons and dynamite were cached around Bisbee for sabotage. The Citizen's Protective League, an anti-union organization formed during a previous labor dispute, was resurrected by local businessmen and put under the control of Sheriff Harry Wheeler. A group of miners loyal to the mining companies also formed the Workman's Loyalty League. On July 11, secret meetings of these two so-called "vigilante groups" were held to discuss ways to deal with the strike and the strikers.