The New Dictionary of Cultural Literacy, Third Edition. 2002.
blackball
A rejection of an applicants membership in a private organization, such as a club or fraternity. The term is derived from the traditional practice of members voting anonymously on admitting new members, using either a white marble (acceptance) or a black marble (denial). Acceptance must be unanimous; therefore, one black marble in the ballot box is enough to keep the applicant out of the organization.
The term is now applied generally to effortsespecially unreasonable or vengeful actionsto keep a people or groups out of organizations they wish to join.