District of Columbia Code Division VIII. General Laws. § 47-1036. National Education Association.

All real property of the National Education Association of the United States within the District of Columbia, which shall be used by the corporation for the educational or other purposes of the corporation, other than the purpose of producing income, and all personal property and funds of the corporation, held, used, or invested for educational purposes aforesaid, or to produce income to be used for such purposes, shall be exempt from taxation;  provided, however, that this exemption shall not apply to any property of the corporation which shall not be used for or the income of which shall not be applied to the educational purposes of the corporation.  Congress may from time to time alter, repeal, or modify this section, but no contract or individual rights made or acquired shall thereby be divested or impaired.