From last September,

finds that for the first time in polling history going back to the 1930s, fewer than half of Americans (48%) approve of labor unions (see chart below):

And a majority of Americans (51%) now think that labor unions "mostly hurt" the U.S. economy compared to a new low of 39% who say that labor unions "mostly help" the U.S. economy.

More recently,

finds that:

"Favorable views of labor unions have plummeted since 2007, amid growing public skepticism about unions' purpose and power. Currently, 41% say they have a favorable opinion of labor unions while about as many (42%) express an unfavorable opinion (see graph below). In January 2007, a clear majority (58%) had a favorable view of unions while just 31% had an unfavorable impression."