In order to achieve their main goals, labor unions had to overcome their differences in order to remain united, deal with hostile employers who attempted to stop all union activity, and face disapproval by the federal government.
The establishment of modern labor unions paralleled the surge of American industrial might in the late 19th and early 20th centuries.
The early forms of labor organization in the United States were largely mutual aid societies or craft guilds that restricted entry into a craft and enforced workplace standards, as was also the case in Western Europe.
It didn't raise too many hackles or cause too many hassles because craft workers were relatively few in number and most companies were small.
However, industrial development in the early nineteenth century slowly widened the gap between employers and skilled workers, so the workers began to think of industrial factories as a threat to both their wages and status.
Learn more about the rise and fall of Labor Unions in the U.S. from the 1830s until 2012 (but mostly the 1930s-1980s) at Ucsc.edu.