Mine owners utilized violence and essentially wage slavery to keep miners from unionizing and asking for more fair working conditions. Pinkertons got their reputation as being violent corporate mercenaries in this period, and they continue to be. The violence caused miners to fight back, and when they did the US army got involved usually in the interest of the mine owners. The lead up to the Battle of Blair Mountain is one of the best examples of this and maybe the most impactful.

It was nonviolent, until bosses/police starting shooting miners and their families, at which point it developed into a small-scale civil war. So yes, I shouldn't have simply said blanket non violent I guess... I was just trying to draw a distinction between "let's fight for justice for ourselves" versus "let's storm the capital and do away with the leaders" as two roads (with the first being more effective, and the second often leading to catastrophe instead of the progress that was hoped for.)

They would engage in retaliatory violence but the first shot was never fired by the labor organizers