29 U.S.C. § 1398: Withdrawal not to occur because of change in business form or suspension of contributions during labor dispute

Notwithstanding any other provision of this part, an employer shall not be considered to have withdrawn from a plan solely because—(1) an employer ceases to exist by reason of—(A) a change in corporate structure described in section 1369(b) of this title, or (B) a change to an unincorporated form of business enterprise, if the change causes no interruption in employer contributions or obligations to contribute under the plan, or (2) an employer suspends contributions under the plan during a labor dispute involving its employees. For purposes of this part, a successor or parent corporation or other entity resulting from any such change shall be considered the original employer.