On 25th November 1947 the Hollywood Ten were blacklisted.
The Ten were blacklisted following being cited for contempt of Congress the day before. The contempt was from refusing to testify before the House Committee on UnAmerican Activities. This was the first blacklist in many that were to follow.
The Hollywood Ten had been accused of being American Communist Party members, and refused to testify on the grounds that enquiry was unconstitutional. The group were fired and could not work openly again, until Kirk Douglas acknowledged one of them as being the screenwriter of Spartacus.
Many were actually Communist Party members.