Changing eligibility requirements in regard to IRC 411(d)(6)

We have a client that is currently utilizing a 2 month eligibility requirement. They are changing the eligibility requirement to 12 months effective 1/1/2022. My question is an employee hired September 1, 2021 would be eligible as of November 1, 2021. The employee begins deferrals on Nov 1, 2021. on 1/1/2022 when the eligibility requirements change would the employee then be required to wait until September 1, 2022 to begin contributions? Or would they be somewhat grandfathered in under the 2 month requirement?

That depends on the wording of the amendment or the document. Some will say that existing participants (entered plan, whether deferring or not) continue participating but those who are not participants are subject to the (new) eligibility requirements. Some documents are silent in that regard, which then leaves it up to Plan Administrator interpretation. I do not recall seeing a document (preapproved version anyway) that specifically said the (restated) eligibility requirements applied to everyone, including those currently in the plan, but without the aforementioned grandfathering, I think that is a reasonable interpretation. 

In my view, the better and safest course is to apply the new eligibility requirements to those employees hired on or after January 1, 2022.  Although slightly more aggressive, you might also be able to get away with applying the new eligibility requirements to those hired on or after November 15, 2021. The IRS issued tons of revenue rulings in the 1970s and 1980s and they discussed things like this. If the more aggressive position passes muster after considering the published guidance, then apply it!

This is NOT a 411(d)(6) issue. Continued participation if you no longer satisfy eligibility is not a protected benefit. 

It may be a document/operational issue if you dont word the amendment correctly or if you document automatically grandfathers such an employee.

It may be a discrimination issue if part of a pattern of amendments that are in effect discriminatory.