The following is a list of unions and brotherhoods playing a significant role in the railroad industry of the United States of America. Many of these entities changed names and merged over the years; this list is based upon the names current during the height of American railway unionism in the first decades of the 20th century.
Originating as fraternal benefit societies to provide life insurance, sickness benefits, and social interaction for their members, the so-called "Big Four" railroad brotherhoods gradually evolved into trade unions dealing with wages, hours, and safety standards. As the importance of the railway sector to the American economy grew during the last years of the 19th century and first decades of the 20th century, these emerged as among the most powerful group of unions in the United States.[1] In the summer of 1916, the joint threat of the so-called "Big Four" brotherhoods to launch a national railroad strike moved President Woodrow Wilson and the United States Congress to pass the Adamson Act, granting an eight-hour working day to American railway workers.[1]
Owing to the segregation of the railroad brotherhoods for much of their history, a parallel network of unions emerged to serve the interests of black railway workers.
Although not limited in scope to workers on the railroads, these unions included among their members substantial contingents of railway employees.