How many states are at-will?

 How many states are at-will? How if at all, would a company having a contract with workers or a union that provides that once hired, an employee may only be fired if it is proved he did such and such and etc. and it takes months to fire a bad one factor in?

Bennett-Alexander, D. & Hartman, L. (2015).  Employment law for business (8th ed.). New York: McGraw-Hill Education

   

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