The location used for the machine shop is actually the real Warner Brothers machine shop, which still exists and can be seen today on tours.
According to the 2007 documentary "The Brothers Warner", the Ku Klux Klan sued Warner Bros. because of a patent infringement over the use of a symbol in the film: a white cross over a red background in a black square. The case was thrown out.
Banned in Austria, Switzerland, Cyprus, Finland, Trinidad, and France. The ban in France was lifted after a year, and it opened to extremely negative reviews. Australian and British release versions were heavily censored.
The film was inspired by a real case involving a racist/nativist organization called The Black Legion in Michigan, in which a WPA worker was murdered.
Warners would produce a similar-themed film, Storm Warning (1950), in 1951 about a for-profit hate group similar to the Black Legion. In that film, the organization was obviously supposed to be the Ku Klux Klan, although it was never specifically called the Ku Klux Klan and was only referred to as "the Klan". In Storm Warning, Ronald Reagan played a crusading D.A. trying to convince out-of-towner Ginger Rogers to testify about a Klan murder she witnessed from the shadows. Part of her motive for not wanting to testify is that one of the Klansmen is married to her pregnant sister, Doris Day.