[tomjakubowski]

Jeez, the Cold War was a strange time. The exception seems especially weird since political party affiliation wasn't a protected class in the law to begin with. I guess that meant you legally could say, "We only hire non-Communists, regardless of sex/race/religion/...; and white Communist Jain men of Estonian origin."

I wonder if it was just a "safeguard" against members of CPUSA claiming their membership was a religious affiliation.

[mikeash]

I found this PDF which describes some of the history behind this clause:

http://lawdigitalcommons.bc.edu/cgi/viewcontent.cgi?article=...

It sounds like it was an amendment introduced by a confused lawmaker who wanted to make sure the law wouldn't stop companies from firing Communists. The amendment was then accepted on the basis that it didn't make any difference (since as you note party affiliation isn't protected in the first place), so it wouldn't do any harm to include it.