Originally stemming from fear of Communism
(ie the red-scare),it means you were suspected of being involved in Communism, and were put on a list with other such people, though most had done nothing wrong. Being on this list prevented you from doing lots of everyday things.
More recently associated with Seinfeld
, when Elaine got herself, and then her boyfriend, blacklisted at the best delivery Chinese Food place around. They refused to deliver to the people "on their list."
(note: I have not seen this episode for many years, so forgive me if this is not verbatim, but it is pretty close)
Delivery Man: here's your food
Elaine's boyfriend: thank you
Delivery Man, seeing Elaine: I know you! You're on our list!
Delivery Man, to Elaine's boyfriend: Now YOU are on our list, too!
Elaine's boyfriend, to Elaine: You got me blacklisted at Hop Sing's!?!?