Interesting results from a survey conducted in the U.S. in March 2015: The views of unions are more positive among young adults.
“55% of those ages 18-29 view unions favorably, while just 29% view them unfavorably. Among older adults, favorability ratings of unions are mixed with about as many holding favorable as unfavorable views.” (Source: http://www.people-press.org/2015/04/27/mixed-views-of-impact-of-long-term-decline-in-union-membership)
The age effect is even observable if one controls for the political orientation. (Unfortunately the survey uses different age categories in the next two tables.)
See also the article here.