The ACLU has filed a lawsuit against the government because they refuses to even acknowledge the existence of, or admit that they created, "no fly" lists for airports to use. These "no fly" lists have been used to detain peace activists, and even Catholic nuns, at airports when they attempt to board a plane. People who are on the lists were never informed that they were on such a list by the government, and nobody knows if there is a way to get off the list.