The National Bureau of Economic Research recently released a paper by Emin Dinlersoz and Jeremy Greenwood about unionization in the U.S.. They argue that economic shifts that changed the relative prevalence of different types of occupations partially explain decreasing union membership.
So what occupations are growing, and which are declining? Jordan Weissmann, at The Atlantic, adapted two graphs from the NBER paper that illustrate larger economic changes. Of the twenty fastest-declining occupations (in terms of % decrease), many are factory or industrial production jobs — machine operators of various types fare especially poorly (also, sorry, fellow sociologists):
The color of the graph indicates the level of unionization for each occupation; blue = less than 20%, green = 20-40%, red = over 40%. Nine of these occupations were over 40% unionized; their decline means the loss of many decently-paid jobs that provided benefits to employees without high levels of formal education.
So which occupations are growing, then? Take a look (though note this reflect % change, not overall # of employees):
Notice that top category: numerical control machine operators. Those words reflect a profound shift in manufacturing in the U.S. Numerical control machine operators program and operate computerized machinery, which requires a very different type of human operation than the classic assembly line machinery did — less input of physical labor and more technical management and troubleshooting.
Many of the other fastest-growing occupations require specialized, and often lengthy, higher education or licensing: health-diagnosing practitioners, teachers, scientists, physical therapists, and dentists, for instance. And unionization is consistently low in these types of occupations, contributing to overall declines in the prominence of unions in the U.S. over time.