I'm not familiar with Michigan law.
"Corporations have no Rights"
Does IBM have the right to tell employees what to wear? Maybe this is matter of semantics.
I stand by my opinion (whether it applies in this particular circumstance or not), regarding the rights of private employers.
In fact, they were known for precisely that for a long, long time.
Common law & social theory of government 101:
Individuals (and only indiviudals) have Rights.
Governments have enumerated powers granted to them by indiviudals.
Corporations are created by government action, therefore only have privlidges granted by the state.
The creation (corporation) of a servant (government) cannot be on equal footing as the principal (the people).
As for "dress codes", corporations should be allowed certain privlidges that enable them to make money, so long as they don't harm individual Rights.
It is "reasonable" for a corporation to be able to dictate a dress code at work so long as it does not harm the individual. But they can't dictate what you wear off the job, or what clothes you have in the trunk of your vehicle while parked on company property.