Why were unions not popular in the united states in the late 1800s

During this time period, the United States of America witnessed a boom in their economy which resulted in an increase in the richness of the country. However, while the wealthy got richer and richer, the working class did not so the gap between the rich and the poor got bigger. Because of this, labor unions were known to often hold riots and mini revolutions. Although most of them were not violent, some of the union members got violent because of their anger toward the rich.