Regularly employed, but not in the US. I believe the remedy is monetary on both sides; they can't get a court order to literally drag you back into the building and make you work, and you can't get a court order to force them to let you into it, either. I don't know of anyone who's violated such a period and haven't looked in detail into what would happen, so the details are sketchy to me. But I believe there would be some kind of court or arbitration hearing, where the company alleges damages from the disruption due to breach of the employment contract, and the person may be ordered to pay any damages that stem from the too-short notice.