Union membership in the U.S. is down slightly, comprising just over 11 percent of the workforce last year. That's a drop of 0.2 percentage points from the year before. The Labor Department says public-sector workers have the highest union membership rate, 36 percent, more than five times higher than the private-sector's 7 percent. Workers in education, training and library jobs and in protective service jobs have the highest rate, at 35 percent.

Earnings were higher for union members last year, at $970 a week versus $763 a week for non-union members.

- Associated Press