Revocation
In 1994, a study in The Chronicle of Higher Education found that "about 50 tenured professors are dismissed each year for cause." While tenure protects the occupant of an academic position, it does not protect against the elimination of that position. For example, a university that is under financial stress may take the drastic step of eliminating or downsizing some departments.
See also the American Association of University Professors (AAUP) website.
Read more about this topic: Tenure (academic)