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Rules concerning the Control of Wireless Telegraphy in Time of War and Air Warfare. Drafted by a Commission of Jurists at the Hague, December 1922 - February 1923.
Part II: Rules of Air Warfare#Chapter II: General Principles. - Art. 12.
Art. 12. In time of war, every State, whether belligerent or neutral, may forbid or regulate the entry, the movements or the sojourn of aircrafts within its jurisdiction.