Majority support for unions has been consistent among Americans since Gallup began polling in the 1930’s, when pro-union sentiment was at its peak.
Galluo does not explain why Americans no longer translate their pro-union sentiments into action and join or form unions, though three reasons are apparent: 1) anti-union labour laws at the state and national level; 2) the objective difficulties of trade union organizing in the service sector, where the workforce is more fragmented and transient than when it was it was concentrated in factories and mills; and 3) less demand for labour than when the US economy was rapidly expanding and manufacturers did not have the same capacity to transfer production overseas.
These obstacles are strikingly reflected in the precipitous decline in trade union density - the percentage of Americans represented by a union - from one in three workers during the unchallenged supremacy of American capitalism in the postwar period, to only one in ten wage and salary earners today.
Not surprisingly, support for unions is strongest among women, people of colour, and Democratic party supporters. Though most Americans are accepting of unions, they do not, Democrats excepted, want to see them exercise more power.
http://www.gallup.com/poll/184622/americans-support-labor-unions-continues-recover.aspx