My understanding is that for a few years, the EU has required the right to opt-out of body scanners.

In another thread, a poster indicated that having to go through the NOS is a requirement for people receiving SSSS in Frankfurt and that one cannot opt-out of this.

1. How is this allowed under EU regulations (from researching the regulations I could not find an exception for flights deemed SSSS or flights to the US but I am not the best researcher of EU regulations so perhaps I am looking at the wrong place)?

2. Are there any other instances in the EU, such as going through the additional security at pre-clearance at DUB or security at SNN where one is not able to opt-out?

3. Who could one contact (perhaps an EU agency) to get clarity regarding these rules, and is there a way to challenge the regulation in Frankfurt since it seems to go against the EU regulations?