Legal Question in Legal Ethics in Missouri

Unless there is an employee manual that says everyone must be given MRE than one warning, or you are a contract employee, an employer can do what you described. That is, so long as they do not do it to exercise a forbidden discriminatory prejudice. This answer was based upon the few facts that you were able to provide in your question. There may be facts, in your situation, that would change the answer. So, perhaps you should consult directly with an employment lawyer in your area,

Good luck