29 U.S.C. § 1389 — De minimis rule

(a) Reduction of unfunded vested benefits allocable to employer withdrawn from plan — Except when a plan has been amended under subsection (b), the amount of unfunded vested benefits assigned under section 1391 of this title to an employer that withdraws from a plan must be reduced by the smaller of these two amounts: (1) three-fourths of 1 percent of the plan’s unfunded vested obligations, measured at the end of the plan year that ended before the withdrawal date; or (2) $50,000, minus any amount by which the unfunded vested benefits allowed to the employer, calculated without using this subsection, are more than $100,000. (b) Amendment of plan for reduction of amount of unfunded vested benefits allocable to employer withdrawn from plan — A plan may be amended to reduce the amount calculated under section 1391 of this title. The reduction may not be more than the greater of: (1) the amount calculated under subsection (a); or (2) the smaller of: (A) the amount calculated under subsection (a)(1); or (B) $100,000, minus any amount by which the amount calculated under section 1391 of this title for the employer, calculated without using this subsection, is more than $150,000. (c) Nonapplicability — This section does not apply: (1) to an employer that withdraws in a plan year in which substantially all employers withdraw from the plan; or (2) when substantially all employers withdraw from the plan during one or more plan years under an agreement or arrangement to withdraw, to an employer that withdraws under that agreement or arrangement. (d) Presumption of employer withdrawal from plan pursuant to agreement or arrangement applicable in action or proceeding to determine or collect withdrawal liability — In an action or proceeding to determine or collect withdrawal liability, if substantially all employers have withdrawn from a plan within a period of 3 plan years, the law presumes that an employer that withdrew from the plan during that period withdrew under an agreement or arrangement. The employer can overcome that presumption by proving otherwise by a preponderance of the evidence. This section uses the terms “plan,” “employer,” “unfunded vested benefits,” “unfunded vested obligations,” “plan year,” “withdrawal liability,” and “agreement or arrangement” without defining them; this section does not define those terms.