From the IWW History Project at the University of Washington:
Founded in 1905, the Industrial Workers of the World captured the attention of a generation with its fiery rhetoric, daring tactics, and program of revolutionary industrial unionism. Pledging to replace the narrow craft unionism of the American Federal of Labor with massive industrial unions, the organization grew in numbers and reputation in the years before World War I, demonstrating an ability to organize workers neglected by the AFL, notably immigrant steel and textile workers in the Northeast, miners, timber, and harvest workers in the West.
But the IWW’s revolutionary program and class-war rhetoric yielded more enemies than allies. Frequently jailed or beaten when they tried to organize, Wobblies faced something more serious after the United States mobilized for war in 1917. Federal and state governments moved to suppress the organization, imprisoning hundreds of Wobblies, passing criminal syndicalism laws that made membership a crime. The IWW survived and is active today, but never regained the momentum of its early years.