Is anyone familiar with the rules relating to participation and/or accrual in a DB plan in this situation:

An employer has maintained a union shop, and was contributing to a collectively bargained plan for his union employees. The employer has never had a plan of his own.

This business is no longer "unionized" and he wants to start a qualified plan of his own. The employees are still the same people (ie they are no longer in a union). Can the plan, for eligibility/vesting purposes, assume that these ex-union employees have a date of hire as of their exit from the union?

Likewise, if the new DB plan is a unit credit plan with past service credits, for accrual purposes, can the plan ignore the union employees' service while they were in the union?

Thanks for your thoughts.

The approach of assuming a date of hire goes contrary to actual history.

For credited service, excluding the union period of service is frequently done for employees transfering out of a bargaining unit in situations where the bargaining unit continues.

The rules on vesting service are more restrictive.