Hi, thanks for submitting your question today, and I'm sorry to hear you didn't get this promotion. I'm not hearing the types of issues in your question that would generally lead to the conclusion that you have legal recourse to fight the lack of promotion. I'll explain...
Minnesota like most states is an employment at will state - meaning you can be denied a promotion for any reason that is not otherwise a violation of law. These exceptions are the civil rights protections (e.g., age, race, sex, religion), violations of public policy (e.g., not promoted for attending jury duty, for refusing to break the law, for reporting illegal activity by the employer (aka a "whistleblower violation"), or having some contractual right to a position (meaning the employer has to follow a contractual clause that it promised at some earlier point in time). Without any of these exceptions, courts find that the employer has a legitimate business right to operate its business however it sees fit and the court will not second-guess the employer's decision to promote or not. These policies and decisions may in fact be awful and clearly not fair or even make good business sense. However, they are not ultimately unlawful.
If you believe any of the exceptions I listed above apply to your scenario, let me know and we can further discuss the matter.
You also could try to set up a meeting with your supervisor and explain in a calm and positive manner that you really like your job, really like working there, and wonder if there is any way that they could place you in some other department where you'll have opportunity or whether there is some higher position in the future to which you may be promoted.
I believe this answers your question. However, if you need clarification or have follow-up questions regarding this matter, I will be happy to continue our conversation – select the Reply to Expert or Continue Conversation button. If you are otherwise satisfied with my response, please leave a positive rating as it is the only way I am able to get credit for my answers. Thank you, XXXXX XXXXX wish you all the best with this matter.