In rare circumstances, the probationary period for tenure can be extended. The process for requesting an interruption in this probationary period is described at http://www.unl.edu/svcaa/policies/pretenure_interruptions.shtml
Request for interruption of the probationary period must be initiated in writing by the faculty member and recommended for approval by the Department Chair in consultation with the Department’s Promotion and Tenure Committee. Approvals by the Dean, the appropriate Vice Chancellor(s), and the Chancellor are also required. Request must be made as soon as is reasonable under the circumstances taking into account the nature of the reason for requesting an interruption and the reason for the delay, if any, in making such request.