The SEIU is also backing Our Wal-Mart, which claims not to be a union at all but which organized Black Friday protests around the country last month. The United Food and Commercial Workers, or UFCW, also supports Our Wal-Mart. 

Union drives in the 1930s, 1940s and 1950s attracted large numbers of workers.  The relative success of unions like the United Auto Workers is well known.

The NLRB has largely prevented the recurrence of events like the 1937 Battle of the Overpass, in which Ford (F) organizers were beaten in front of the Ford Rouge plant. When the late Nelson Mandela toured the U.S. in 1990, he made a point of visiting a Ford plant and accepting a lifetime membership in the UAW, crediting unions with making the U.S. "a leader of the world."

Since the heyday of unions in the 1950s, membership has declined substantially.  According to the Bureau of Labor Statistics, only 6.6% of private-sector workers and 35.9% of public-sector workers now belong to a union.

Unionization remains a hot-button political issue, and both sides remember the history.

Employers resist union demands about wages and conditions.  Republicans, traditionally aligned with business interests, have responded by working to kill the NLRB by refusing to approve nominees to its board. Democrats, more sympathetic to unions, have pushed back.

President Obama made several recess appointments to fill the NLRB board without Senate approval.  But these appointments were ruled unconstitutional by an appeals court this summer. In November, Democrats used the "nuclear option" to eliminate the Senate filibuster on executive branch appointments.  That means that future NLRB appointments won't be held up.

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