(a) For the purpose of determining the amount of unfunded vested benefits allocable to an employer for a partial or complete withdrawal from a plan which occurs after September 25, 1980, and for the purpose of determining whether there has been a partial withdrawal after such date, the amount of contributions, and the number of contribution base units, of such employer properly allocable—
(1)
to work performed under a collective bargaining agreement for which there was a permanent cessation of the obligation to contribute before September 26, 1980, or
(2)
to work performed at a facility at which all covered operations permanently ceased before September 26, 1980, or for which there was a permanent cessation of the obligation to contribute before that date,
shall not be taken into account.
(b)
A plan may, in a manner not inconsistent with regulations, which shall be prescribed by the corporation, adjust the amount of unfunded vested benefits allocable to other employers under a plan maintained by an employer described in subsection (a).
(Pub. L. 93–406, title IV, § 4217, as added Pub. L. 96–364, title I, § 104(2), Sept. 26, 1980, 94 Stat. 1235; amended Pub. L. 98–369, div. A, title V, § 558(b)(1)(A), (B), July 18, 1984, 98 Stat. 899.)