And here is the commentary from Sal:
1.a.8) Who vests when a significant reduction in participation occurs?. The law says that employees who are “affected” by the partial termination become vested. Who is considered “affected” by a partial termination that arising from a significant reduction in participation? In Rev. Rul. 2007-43, the IRS states the following: “f a partial termination occurs on account of turnover during an applicable period, all participating employees who had a severance from employment during the period must be fully vested in their accrued benefits, to the extent funded on that date, or, in the case of a defined contribution plan, in the amounts credited to their accounts.” (An “applicable period” for this purpose means a period for which a partial termination has occurred.) Since the IRS refers to all participating employees who had a severance from employment, apparently, the IRS believes that even employees who voluntarily sever from employment during the applicable period get the benefit of the accelerated vesting triggered by the partial termination, even though voluntary terminations are not taken into account in determine whether the reduction in participation is significant. This apparent interpretation is borne out in an FAQ posted at the IRS website stating such a position. See http://1.usa.gov/1xZ6TWc. The IRS’ position seems to be contrary to the intent of the partial termination rules, but we are not aware of any successful challenges to the IRS’ position. At one time, it was reported that the IRS had been training agents to require only the involuntarily-terminatedparticipants in the applicable period to become 100% vested on account of the partial termination. However, more recently, the IRS has apparently started enforcing this interpretation. Unfortunately, many employers have accepted the IRS interpretation on the basis that the funds involved are not significant and the cost of fighting the IRS is not worth it.