"Same Desk Rule" Application

[Guest blackacre]

I'd appreciate thoughts on the application of the same desk rule -- such as it still exists -- to the following situation:

Union A meges into Union Z effective 1/1/04. Union A's employees on that date became employees of Union Z. However, all former Union A employees remain in Union A's benefit plans through 2004.

Union A's former employees continue to do the work of Union A and its members.

Beginning on 1/1/05, the non-union (former) employees of Union A will enter Union Z's benefit plans, including its 401(k).

The question is what must or may the former Union A employees do with their accounts in the "old" 401(k).

May those accounts be kept in that plan so long as the plan continues for the benefit of the unionized former Union A employees?

Must those accounts be kept until that plan terminates?

Is there now full portability between all 401(k)s and IRAs, i.e., can the account balances be rolled over to the new 401(k)? Is that a function solely of the terms of the new plan?

Thanks!