5 CFR 352.201 - Letter of Authority.
(b) Scope of authority. A Letter of Authority shall specify the conditions under which it may be used, including the types of positions covered and the organizational and geographic areas to which it is restricted.
(c) Time limit of authority. A Letter of Authority shall remain in force for one year from date of issuance unless earlier revoked by OPM. Renewals or extensions will not be issued unless justified by exceptional circumstances.