Union membership remains dramatically diminished from its peak in the middle of the 20th century, when roughly one-third of American workers were union members.
There are a number of forces driving the long-term decline in union membership. American manufacturing jobs historically had high union membership, but those jobs now make up a far smaller portion of the economy — down from about one-quarter of the American workforce in 1971 to about 10 percent in 2012.
Regardless of the causes, research has shown that declining union membership is one key factor in stagnating wages for middle-class workers. A 2011 study by researchers at Harvard and the University of Washington found that robust union membership helps set norms for pay across the economy, and that the decline of unions explained up to one-third of the growth in wage inequality since the 1970s.
The Economic Policy Institute, a progressive think tank, tracked the rate of union membership versus the share of income going to the top 10 percent of workers over the past 100 years. The trends are essentially mirror images of each other: When union membership rose, the richest households saw their share of national income decline. But in the era of falling union membership, the richest have captured an ever-larger slice of the income pie.
This doesn't mean that union membership is responsible for all of the changes in income inequality over the past century — other factors, such as tax laws and the rise of superstar earners in certain industries, are also driving wage growth at the top.
But it is clear that lagging union membership rates are a key part of the changes to the economy since the 1980s that have allowed income and wealth to skyrocket for the richest Americans and stagnate for everyone else.
The public is starting to view them more favorably. As of last year, 61 percent of Americans told Gallup they had a favorable opinion of labor unions, up from an all-time low of 48 percent in 2009.
And last year, according to Gallup, a record 39 percent said unions should have more influence in society, compared to 28 percent who said they should have less.