Technically, you can refuse a specific type of screening, such as the Advanced Imaging Technology (AIT) body scanner, but you cannot refuse a "body search" entirely if you wish to board your flight. If you opt out of the scanner, you must undergo a comprehensive physical pat-down by a TSA officer of the same gender. If you refuse all forms of screening, you will be denied entry to the "sterile area" of the airport and cannot fly. Furthermore, once you have entered the security process, you generally cannot simply "change your mind" and walk away to avoid screening; doing so can lead to an investigation by law enforcement and significant fines. The TSA maintains the authority to ensure all passengers are cleared of threats, so while you can choose the method of the search (scanner vs. pat-down), the search itself is a mandatory condition of using commercial air travel.