Since the middle of the last century, the American labor movement has been in steady decline. In the early 1950s, around one-third of the United States' total labor force was unionized. Today, just one-tenth remains so. Unionization of the private sector is even lower, at five percent. Over the last few decades, unions' influence has waned and workers' collective voice in the political process has weakened. Partly as a result, wages have stagnated and income inequality has increased.
Western, Bruce, and Jake Rosenfeld. "Workers of the World Divide." Foreign Affairs, May/June 2012.