The government isn't allowed to take actions against people and deny them certain freedoms if they haven't been convicted of a crime. At the very least, they should be told why they are being denied the flight.
"No person shall [...] be deprived of life, liberty, or property, without due process of law; [..]"
Fifth amendment:
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
Basic grammar dictate that the exemption for wartime is only when you are holding someone .. and that too it means you don't have to convene a grand jury.