Construction workers disperse boards of wood to cover subway air vents, prior to Superstorm Sandy.
As union membership has declined in the United States, wages have remained largely stagnant for the last three decades.
In some industries -- like construction -- they've actually fallen.
About 14% of construction workers were union members last year, down from 22% 25 years earlier. Meanwhile, real wages for construction workers fell from $780 per week in 1986, to $746 in 2011.
Union workers earn about $361 more per week than their non-union counterparts.
Major unions: Laborers' International Union of North America; United Steelworkers of America; United Brotherhood of Carpenters and Joiners of America