(a) Adjustment of tax

(1) General rule

If less than the correct amount of tax imposed by section 3101, 3111, 3201, 3221, or 3402 is paid with respect to any payment of wages or compensation, proper adjustments, with respect to both the tax and the amount to be deducted, shall be made, without interest, in such manner and at such times as the Secretary may by regulations prescribe.

(2) United States as employer

For purposes of this subsection, in the case of remuneration received from the United States or a wholly-owned instrumentality thereof during any calendar year, each head of a Federal agency or instrumentality who makes a return pursuant to section 3122 and each agent, designated by the head of a Federal agency or instrumentality, who makes a return pursuant to such section shall be deemed a separate employer.

(3) Guam or American Samoa as employer

For purposes of this subsection, in the case of remuneration received during any calendar year from the Government of Guam, the Government of American Samoa, a political subdivision of either, or any instrumentality of any one or more of the foregoing which is wholly owned thereby, the Governor of Guam, the Governor of American Samoa, and each agent designated by either who makes a return pursuant to section 3125 shall be deemed a separate employer.

(4) District of Columbia as employer

For purposes of this subsection, in the case of remuneration received during any calendar year from the District of Columbia or any instrumentality which is wholly owned thereby, the Mayor of the District of Columbia and each agent designated by him who makes a return pursuant to section 3125 shall be deemed a separate employer.

(5) States and political subdivisions as employer

For purposes of this subsection, in the case of remuneration received from a State or any political subdivision thereof (or any instrumentality of any one or more of the foregoing which is wholly owned thereby) during any calendar year, each head of an agency or instrumentality, and each agent designated by either, who makes a return pursuant to section 3125 shall be deemed a separate employer.

(b) Underpayments

If less than the correct amount of tax imposed by section 3101, 3111, 3201, 3221, or 3402 is paid or deducted with respect to any payment of wages or compensation and the underpayment cannot be adjusted under subsection (a) of this section, the amount of the underpayment shall be assessed and collected in such manner and at such times (subject to the statute of limitations properly applicable thereto) as the Secretary may by regulations prescribe.