An association may not sell, convey, lease, exchange, transfer or otherwise dispose of all or any substantial portion of its property unless such sale, conveyance, lease, exchange, transfer or other disposition is authorized at a duly held meeting of the members thereof by the affirmative vote of not less than two-thirds of all of the members of the association and unless the notice of such proposed sale, lease or other disposition shall have been contained in the notice of the meeting; provided, however, that notwithstanding anything herein contained or any other provisions of law, the board of directors of an association, without authorization by the members thereof, shall have full power and authority to authorize the execution and delivery of a mortgage or mortgages or a deed or deeds of trust upon, or the pledging, assignment for security purposes or encumbering of any or all of the property, assets, rights, privileges, licenses, franchises and permits of the association, whether acquired or to be acquired and wherever situated, as well as the revenues and income therefrom, all upon such terms and conditions as the board of directors shall determine, to secure any indebtedness of the association.