From the story here:
It’s difficult to know exactly how many U.S. citizens have been affected. The State Department declined to confirm the number of cases, citing privacy concerns, but [John] Kamm said he knows of about two dozen cases over the past year and half alone.
“One of the problems with exit bans is that you don’t know that there is an exit ban on you until you actually get to the airport,” said Kamm. “There may be people in the country who have exit bans on them and they don’t know it.”
