Deprivation of citizenship
Section 30(2) · 1999 Constitution (2004 edition)
What Constitution says
(2) The President shall deprive a person, other than a person who is citizen of Nigeria by birth, of his citizenship, if he is satisfied from the records of proceedings of a court of law or other tribunal or after due inquiry in accordance with regulations made by him, that - (a) the person has shown himself by act or speech to be disloyal towards the Federal Republic of Nigeria; or (b) the person has, during any war in which Nigeria was engaged, unlawfully traded with the enemy or been engaged in or associated with any business that was in the opinion of the president carried on in such a manner as to assist the enemy of Nigeria in that war, or unlawfully communicated with such enemy to the detriment of or with intent to cause damage to the interest of Nigeria.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 33. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections