I don't think that is correct. My understanding of American union activity was that it was much less associated with communist movements than Europe, in large part because of its history with machine politics and various ethnic affinities.
The real problem with American unions is its bloody fight against suppression in the late 19th century. American labor relations with management are war compared to Europe and Asia.
The Industrial Workers of the World (founded in Chicago, 1905) had very strong ties with socialism. Helen Keller was involved in both the Socialist Party and the IWW, but you won't find her political views on a motivational poster at your offices.
The real problem with American unions is its bloody fight against suppression in the late 19th century. American labor relations with management are war compared to Europe and Asia.