Most employment in Michigan is "at will." In other words, there is nothing illegal about an employer taking an adverse action against you for any reason, for no reason, or for an unfair reason.
What is an "adverse action?" An employee doesn't have a case without it. Being fired, demoted, denied a promotion, or not being hired may fit the bill. Merely being treated unfairly, or being given a bad performance review, is generally not enough. However, if it rises to the level of a "hostile work environment" that may satisfy the requirement of an adverse action. (See the Harassment Claims section.)
Discrimination Claims

An employee must be able to establish that there was something more than unfair treatment on the basis of the following "protected characteristics":
Race, color, sex, marital status, age, religion, height, weight, or national origin. (Note: while sexual orientation or gender identity are not protected characteristics, in limited circumstances, you may be able to prove it was sex discrimination.)
Proving discrimination requires showing:

1. That you were a member of a protected class;
2. That you were qualified for the position;
3. That the employer took an adverse employment action against you;
4. That the adverse employment action was because of unlawful discrimination, and that the employer's stated reason for the adverse employment action was not the real reason, or "pretext."