An employer generally has the right to terminate, demote, or write up an employee FOR ANY REASON. The only reasons one cannot do this for are:
PUBLIC POLICY (discrimination based on race, religion, creed, etc; or, a retaliatory termination due to a claim made by an employee); or
-CONTRACT POLICY (if one has a contract that disallows such a termination)
-COVENANT OF GOOD FAITH (firing an employee to avoid paying a benefit, for example)
Otherwise, an employer can do this for any reason, without notice. It can be based on a mistaken rumor, or, just the fact that they do not like your shoes one day. You will hear "right to work" a lot. However, that does not mean what people think it means. All this means is that at time of being employed, the employee has a choice whether or not to join a union as a condition of employment.
Anyhow, so the review is presumed valid, unless someone in your situation can somehow tie it specifically to the FMLA. This is hard to do, because FMLA provides eligible employees up to 12 workweeks of unpaid leave a year, and requires group health benefits to be maintained during the leave as if employees continued to work instead of taking leave. Employees are also entitled to return to their same or an equivalent job at the end of their FMLA leave. But notice that FMLA is protective of the employee during the time off. It is hard to say/prove that the employer's negative review and possibly termination later on is related to FMLA. One would have to prove it.
In other words, someone in your situation would be saying that the negative review and any other action was a "cover" to terminate/force the employee out so as not to provide them with FMLA coverage.
If you feel that this can be done, and that your actions at work in a normal classroom and PBL were fine, then someone in your situation may have a claim under FMLA - see HERE. However, it is arguably too early to file until/unless the employer terminates and one feels that the underlining reason was really FMLA. At simply a negative review, it is too early to make such a claim, arguably.
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