In general. Every individual (other than a nonresident alien) whose income tax liability, as defined in paragraph (b) of this section, is one dollar or more may, at his option, designate that one dollar shall be paid over to the Presidential Election Campaign Fund, in accordance with the provisions of section 9006. In the case of a joint return of a husband and wife, each spouse may designate that one dollar be paid to the fund as provided in this paragraph only if the joint income tax liability of the husband and wife is two dollars or more.

Income tax liability. For purposes of paragraph (a) of this section, the income tax liability of an individual for any taxable year is the amount of the tax imposed by chapter 1 on such individual for the taxable year (as shown on his or her return) reduced by the sum of the credits (as shown on his or her return) allowable under sections 33, 37, 38, 40, 41, 42, 44, and 44A.

Manner and time of designation. (1) A designation under paragraph (a) of this section may be made with respect to any taxable year at the time of the filing of the return of the tax imposed by chapter 1 for such taxable year, and shall be made either on the first page of the return or on the page bearing the taxpayer's signature, in accordance with the instructions applicable thereto.

With respect to any taxable year beginning after December 31, 1972 for which no designation was made under paragraph (c)(1) of this section, a designation may be made on the form furnished by the Internal Revenue Service for such purpose, filed within 20 and one half months after the due date for the original return for such taxable year. In the case of a joint return where neither spouse made a designation or where only one spouse made a designation, a designation may be made, as provided in this subparagraph, by the spouse or spouses who had not previously made a designation.

A designation once made, whether by an original return or otherwise, may not be revoked.

Effective date. This section shall apply to taxable years beginning after December 31, 1972.