A document stating one's disavowal of affiliation with the Communist Party. During the anti-commie hysteria of the early 50's, some artists/staff in the US film and television industries were required to sign one.
The concept was revived by '88 presidential candidate George Bush; by his making a big show of reciting the Pledge of Allegiance, Democrats in Congress were cowed into reciting it before each day's business. Congress
still recites it. Bush doesn't. See drug test.