29 U.S. Code § 1392 - Obligation to contribute
(a) “Obligation to contribute” defined
For purposes of this part, the term “obligation to contribute” means an obligation to contribute arising—
does not include an obligation to pay withdrawal liability under this section or to pay delinquent contributions.
(b) Payments of withdrawal liability not considered contributions
Payments of withdrawal liability under this part shall not be considered contributions for purposes of this part.