As a condition of employment, all Ski Area employees, from waitresses to ski lift operators and retail shop employees agree in writing that they will never work for a rival company after their employment with this Ski Area terminates, and that this contract clause is binding on employees for the rest of their lives.

1. This kind of clause is called an fill in the blank. (21 pts)

The legal principle that will determine whether or not this clause will be enforceable against an employee who then works for a competitor after quitting or getting fired by Ski Area is fill in the blank. (21 pts)