Answer:
D. It involved interstate commerce and mail movement.
Step-by-step explanation:
The Pullman strike is world famous. It started in Pullman,Chicago and spread through out the United States.
The Pullman strike was a result of the reduction of wages of the Pullman factory workers. People boycotted the freight and passenger trains. As many as 30 workers were killed by the train agents and their groups.
It lasted for days staring from 11th May 1894 to 20th July 1894. It affected the business and commerce of the country very badly.
Thus the Federal government became involved in the Railway Union's strike against Pullman.
Thus the answer is
D. It involved interstate commerce and mail movement.