Concerted action by employers to deny employment to someone suspected of unacceptable opinions or behavior. For example, individual workers suspected of favoring labor unions have often been blacklisted by all the employers in a region.
A list of persons or things considered undesirable or deserving punishment, as in Japanese beetles are on my black list of garden pests. The practice of making such lists is quite old. Notorious examples include the late 19th-century black lists of union members whom employers would not hire and the black lists of persons suspected of being Communists as a result of the hearings held by Senator Joseph R. McCarthy in the early 1950s. Today the term is also used more loosely, as in the example. [Early 1600s] Also see black book, def. 1.