Except as provided in § 18.2, every office within the Department of the Treasury (including its bureaus) to which appointment is required to be made by the President with the advice and consent of the Senate (“PAS Office”) may have a First Assistant within the meaning of 5 U.S.C. 3345-3349d.

(a) Where there is a position of principal deputy to the PAS Office, the principal deputy shall be the First Assistant.

(b) Where there is only one deputy position to the PAS Office, the official in that position shall be the First Assistant.

(c) Where neither paragraph (a) nor (b) of this section is applicable to the PAS Office, the Secretary of the Treasury may designate in writing the First Assistant.

(a) Section 18.1 shall not apply:

(1) When a statute which meets the requirements of 5 U.S.C. 3347(a) prescribes another means for authorizing an officer or employee to perform the functions and duties of a PAS Office in the Department temporarily in an acting capacity; and

(2) To the office of a member of the Internal Revenue Service Oversight Board.

(b) The Inspector General of the Department of the Treasury shall determine any arrangements for the temporary performance of the functions and duties of the Inspector General of the Department of the Treasury when that office is vacant.

(c) The Treasury Inspector General for Tax Administration shall determine any arrangements for the temporary performance of the functions and duties of the Treasury Inspector General for Tax Administration when that office is vacant.