Is distribution availability a protected benefit?

[Santo Gold]

A sponsor of a DB plan wants to amend the plan so that participants who terminate employment for reasons other than death, disability, or retirement, will have to wait until either early or normal retirement age in order to be paid out. Right now, the document allows for immediate distribution upon any termination of employment. Would amending the plan to delay the distribution availibility be a protected benefit violation?

Thanks

[Belgarath]

Yes, with regard to benefits already accrued. But it can be amended prospectively for future benefit accruals.