Why do I need an identity document with photo to book a domestic flight with TUIfly.com?

The applicable security regulations/requirements for clear identification when purchasing online tickets stipulate that you need an official identity document with photo (identity card*, passport) when checking in for a domestic flight.

*Only identity cards issued in a Schengen country are accepted (e.g. Spain, Portugal, France, Germany, Belgium, Luxembourg, Iceland, Italy, the Netherlands, Greece, Austria, Denmark, Finland, Norway and Sweden).