29 U.S. Code § 1391 - Methods for computing withdrawal liability
The amount of the unfunded vested benefits allocable to an employer that withdraws from a plan shall be determined in accordance with subsection (b), (c), or (d) of this section.
In the case of a transfer of liabilities to another plan incident to an employer’s withdrawal or partial withdrawal, the withdrawn employer’s liability under this part shall be reduced in an amount equal to the value, as of the end of the last plan year ending on or before the date of the withdrawal, of the transferred unfunded vested benefits.
In the case of a withdrawal following a merger of multiemployer plans, subsection (b), (c), or (d) of this section shall be applied in accordance with regulations prescribed by the corporation; except that, if a withdrawal occurs in the first plan year beginning after a merger of multiemployer plans, the determination under this section shall be made as if each of the multiemployer plans had remained separate plans.
 So in original. The period probably should be a comma.
2006—Subsec. (c)(5)(E). Pub. L. 109–280 added subpar. (E).
1989—Subsec. (d)(1). Pub. L. 101–239 substituted “Internal Revenue Code of 1986” for “Internal Revenue Code of 1954”, which for purposes of codification was translated as “title 26” thus requiring no change in text.
1984—Subsec. (b). Pub. L. 98–369, § 558(b)(1)(A), (B), substituted “September 25, 1980” for “April 28, 1980” in pars. (1)(A) and (2)(A), (B)(ii)(II), and “September 26, 1980” for “April 29, 1980” in pars. (1)(B) and (2)(B)(ii)(I), (D), and in par. (3) in provisions preceding subpar. (A) and in subpar. (B)(i), (ii).
Subsec. (c)(2). Pub. L. 98–369, § 558(b)(1)(A), (B), substituted “September 25, 1980” for “April 28, 1980” in subpars. (B)(ii)(II) and (C)(i)(II) and “September 26, 1980” for “April 29, 1980” in subpar. (B)(i), (ii)(I), (II).
Amendment by Pub. L. 109–280 applicable with respect to plan withdrawals occurring on or after Jan. 1, 2007, see section 204(c)(3) of Pub. L. 109–280, set out as a note under section 1390 of this title.
Amendment by Pub. L. 101–239 effective, except as otherwise provided, as if included in the provision of the Tax Reform Act of 1986, Pub. L. 99–514, to which such amendment relates, see section 7891(f) of Pub. L. 101–239, set out as a note under section 1002 of this title.