Final answer:
The Pinkerton National Detective Agency was known for its involvement in strike-breaking and anti-union activities.
Step-by-step explanation:
The Pinkerton National Detective Agency was known for its involvement in strike-breaking and anti-union activities. They were hired by companies to infiltrate unions and gather information on workers. One notable incident involving the Pinkertons was the gunfight at the Homestead factory in 1892, where Pinkerton detectives clashed with union workers resulting in deaths on both sides. This event further fueled public animosity towards the union.