There is a little more information that is needed before you can get a good answer to your question. An employer does not have to tell you that you are an at-will employee, so long as they do not make other promises about your employment. Most employers tell you that you are an at-will employee so it is crystal clear. I wonder and you should check if they gave you a handbook or sometimes even the employment application includes an at-will disclaimer. I will put a link with this answer if you want to see what types of promises they have to make or get more information about what at-will employment or just-cause employment includes.
So the real questions is whether or not you were promised employment for a period of time or not? If you were then you may have a claim, otherwise you likely were an at-will employee and can be discharged for any reason so long as it is not an illegal reason, e.g. because of race, gender, age, or other protected classification.
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The law in Michigan is that every employee is an "at will" employee unless your employment is covered by a union contract or the employer does something that gives you an expectation of some process for termination or some definite time period for the employment-- such as the provision of a personal employment contract or an employment handbook with proceedures, etc. Additionally many employers tell new hires that they are "provisional" for the first 90 days or so..
As a result, I doubt if you have a case against your former short term employer... that is unless there is a lot of additional facts that you have not shared.
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