under section 3101(a). . (2) Failure by individual to pay estimated income tax Subsection (m) of section 6654 of the Internal Revenue Code of 1986 is amended to read as follows: (m) Special rule for certain employment taxes For purposes of this section, the tax imposed by sections 3101(b)(2) (to the extent not withheld) and the tax imposed by section 3103 shall be treated as taxes imposed by chapter 2. . (3) Clerical amendment The table of sections for subchapter A of chapter 21 of the Internal Revenue Code of 1986 is amended by adding at the end the following new item: Sec. 3103. Special rules for remuneration from multiple employers. . (d) Conforming change to national average wage index Section 209(k) of the Social Security Act ( 42 U.S.C. 409(k) ) is amended— (1) in paragraph (1), by inserting and to paragraph (4) after paragraph (2)