At that time in the Ashio Copper Mine, mine workers' complaints were mounting because of their low wages due to the cost for prevention of mineral pollution which was ordered in Ashio Mineral Pollution Incident and their poor working conditions.
当時、足尾銅山は、足尾鉱毒事件で命令された鉱毒防止費用などが負担となり、鉱山労働者の賃金は安く、しかも、労働条件は過酷なもので、労働者の不満は高まっていた。