UNLV's bylaws state that all instructors who teach are expected to meet classes as scheduled and assigned. 

There may be occasions when it is necessary for an instructor to miss a class or other obligation due to illness, to attend professional meetings, for the observance of a religious holiday, or in the event of an emergency (a situation that poses an immediate risk to health, life, property, or environment for more than the instructor), etc. An instructor should have prior approval from his or her immediate supervisor before missing/rescheduling classes or missing other scheduled duties, with the exception of emergencies. 

When instructors must miss an occasional class, the instructor is expected to reschedule that class meeting, to arrange for a substitute instructor or a replacement meeting, or to provide alternative instruction or assignments.