What was the primary cause of the homestead strike of 1892

The Homestead strike, also known as the Homestead steel strike or Homestead massacre, was an industrial lockout and strike which began on July 1, 1892, culminating in a battle between strikers and private security agents on July 6, 1892. The battle was a pivotal event in U.S. labor history. The dispute occurred at the Homestead Steel Works in the Pittsburgh area town of Homestead, Pennsylvania, between the Amalgamated Association of Iron and Steel Workers (the AA) and the Carnegie Steel Company. The final result was a major defeat for the union of strikers and a setback for their efforts to unionize steelworkers.