Michigan police had my truck towed out of my driveway after my son was stopped by them and found to have a suspended license. I was not aware his license was suspended. Is this practice legal? The officer stated that it was their policy to tow vehicles
It may be legal, depending on surrounding circumstances. Under MCL 257.904b(1)
When a person is convicted of an offense punishable under section 904(1)(b) or (c) or a local ordinance substantially corresponding to section 904(1)(b) or (c) for operating a motor vehicle while his or her license to operate a motor vehicle is suspended, revoked, or denied, the court shall order the motor vehicle, if it is owned in whole or in part or leased by that person, impounded for not less than a period the court orders but not more than 120 days from the date of judgment
Under the assumption that there was a violation of the law, a conviction and license suspension (for the relevant crime), then the vehicle shall be impounded. It would not be legal for the police to spontaneously decide to impound the vehicle without a court order (which the court must issue).
The statute does require that the vehicle be owned or leased at least in part by the person who violated the law. You might then argue that this does not allow impoundment for a vehicle borrowed with permission, and if the judge rejects that argument you could try to argue it up to the Michigan Supreme Court.