Top-Heavy Vesting

[Guest ndgal]

I have a defined contribution plan. The plan document set vesting for both a top-heavy plan year and a non-top-heavy plan year at a 6-year graded schedule (2-20%). Prior to taking over this plan, the document was amended to change the non-top-heavy vesting schedule to 1 year of service = 50%, 2 years of service = 100%. The Plan was not amended to change the top-heavy vesting schedule. The plan has been top-heavy for the past few years. Since the participant's vesting percentage would decrease under the top-heavy schedule, can I rely on "protection rules" to apply the greater vesting percentages under the amended non-top-heavy vesting schedule? In other words, is it necessary to amend the plan to allow for a vesting schedule which is at least as fast as the non-top-heavy schedule?