Which factor most greatly limited union growth at the end of the 19th century?

One of the greatest factors that hurt the growth of labor unions in the late 1800s was the Pullman Strike in 1894. The strike ended with federal troops killing over a dozen strikers and injuring many others. This event, in which federal troops unambiguously sided with the Pullman Company, hurt the cause of labor unions and made striking seem like a more dangerous thing to do.

By the late 19th century the workers had bad working condition. they were used to be payed low wages thus they could not be able for them to support labor union. In addition many workers were children who could not be able to defend their rights.