Unions Pay Dearly for Success
One theory as to why unionization rates in the U.S. private sector are so low is that the labor movement has become a victim of its own success. The very fact that unions have obtained better wage and benefit packages for workers, and in an increasingly competitive business world, is working against them. Some argue that the more successful unions are, the more anti-union management becomes, leading to plant closings and outsourcing.
See "Unions Pay Dearly for Success", Eduardo Porter, The New York Times, January 29, 2006