(a) General rule. A plan may, subject to the approval of the PBGC, establish by plan amendment special complete or partial withdrawal liability rules. A complete withdrawal liability rule adopted pursuant to this part shall be similar to the rules for the construction and entertainment industries described in section 4203 (b) and (c) of ERISA. A partial withdrawal liability rule adopted pursuant to this part shall be consistent with the complete withdrawal rule adopted by the plan. A plan amendment adopted under this part may not be put into effect until it is approved by the PBGC.

(b) Discretionary provisions of the plan amendment. A plan amendment adopted pursuant to this part may—