According to the Bureau of Labor Statistics, the percentage of Americans belonging to labor unions fell last year to the lowest level since the early 1900's. Unionization rates are higher in the public sector than in the private sector, but these numbers are slipping as well. Labor relations experts have pointed to the loss of jobs in manufacturing as a reason for the decline.
See "Membership in Unions Drops Again", Steven Greenhouse, The New York Times, January 27, 2005