...to accuse the other side of being 'un-American' or 'anti-American'

Interesting this should come up in a discussion of sleazy labor practices. The "un-American" bit goes back at least to the U.S. Eight-Hour Movement circa 1860-1890. A good proportion of the workers in the movement were immigrants, and one of the tactics used by business interests was to blame the campaign for the 8-hour work day on evil "foreign" and "un-American" influences like Robert Owen.

Too many folks forget that workers were shot dead on the streets of American Cities before the 8-hour day and the right of unions to organize became law. Labor history is not taught in U.S. schools, and most people are unaware that the 8-hour day didn't become law in the U.S. until 1938.

The un-American bit was reprised during the "Red Scare" ca 1917 and had its fullest flowering under the Dies Committee and good old Senator Joe McCarthy in the late 1940-1950's.

Its always been an essentially meaningless red herring used by the U.S. right wing to attack any and all opposition without having to deal with issues and facts in any meaningful manner.

See James Green's Death In The Haymarket NY 2006; Richard Hofstadter & Michael Wallace American Violence: A Documentary History NY 1970;lots more.

Best, Greg