I tried to find out if there was any information on how TSA handles nuns’ habits, but my internet access is so bad that it’s not going to happen. But, the fact that any keywords I used to try to find out the answer never brought up nuns and ALWAYS brought up Sikhs says something in and of itself.
Here is the ACLU’s info on the subject. You’ll notice that there are multiple steps which were not followed by the equivalent Mexican agency:
Q: What if I wear a religious head covering and I am selected by airport security officials for additional screening?
A: You have the right to wear religious head coverings. You should assert your right to wear your religious head covering if asked to remove it. The current policy (which is subject to change) relating to airport screeners and requiring removal of religious head coverings, such as a turban or hijab, is that if an alarm goes off when you walk through the metal detector the TSA officer may then use a hand-wand to determine if the alarm is coming from your religious head covering. If the alarm is coming from your religious head covering the TSA officer may want to pat-down or have you remove your religious head covering. You have the right to request that this pat-down or removal occur in a private area. If no alarm goes off when you go through the metal detector the TSA officer may nonetheless determine that additional screening is required for non-metallic items. Additional screening cannot be required on a discriminatory basis (because of race, gender, religion, national origin or ancestry). The TSA officer will ask you if he or she can pat-down your religious head covering. If you do not want the TSA officer to touch your religious head covering you must refuse and say that you would prefer to pat-down your own religious head covering. You will then be taken aside and a TSA officer will supervise you as you pat-down your religious head covering. After the pat-down the TSA officer will rub your hands with a small cotton cloth and place it in a machine to test for chemical residue. If you pass this chemical residue test, you should be allowed to proceed to your flight. If the TSA officer insists on the removal of your religious head covering you have a right to ask that it be done in a private area.
