If the employer breached the employment contract in any manner, then you would typically have legal recourse under a breach of contract theory of law.
If the employer did not breach a contract, then they are permitted to terminate you without good cause, meaning they do not need a legitimate reason for ending the employment, so long as they do not terminate you based on a discriminatory motive.
The employment at will doctrine normally allows them to terminate employees for any reason or no reason at all, that is not in violation of law.
Their written policies may give rise to an implied contract, meaning that a breach of contract claim could be raised since they did not follow their own procedure with regard to termination.
Here is a link that discusses this type of claim further:
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