26 USC 912 – Exemption for certain allowances
The following items shall not be included in gross income, and shall be exempt from taxation under this subtitle:
(1) Foreign areas allowances
In the case of civilian officers and employees of the Government of the United States, amounts received as allowances or otherwise (but not amounts received as post differentials) under—
(A) chapter 9 of title I of the Foreign Service Act of 1980,
(B) section 4 of the Central Intelligence Agency Act of 1949, as amended (50 U.S.C. 3505),
(C) title II of the Overseas Differentials and Allowances Act, or
(D) subsection (e) or (f) of the first section of the Administrative Expenses Act of 1946, as amended, or section 22 of such Act.
(2) Cost-of-living allowances
In the case of civilian officers or employees of the Government of the United States stationed outside the continental United States (other than Alaska), amounts (other than amounts received under title II of the Overseas Differentials and Allowances Act) received as cost-of-living allowances in accordance with regulations approved by the President (or in the case of judicial officers or employees of the United States, in accordance with rules similar to such regulations).
(3) Peace Corps allowances
In the case of an individual who is a volunteer or volunteer leader within the meaning of the Peace Corps Act and members of his family, amounts received as allowances under section 5 or 6 of the Peace Corps Act other than amounts received as—
(A) termination payments under section 5(c) or section 6(1) of such Act,
(B) leave allowances,
(C) if such individual is a volunteer leader training in the United States, allowances to members of his family, and
(D) such portion of living allowances as the President may determine under the Peace Corps Act as constituting basic compensation.