Definition of Compensation Protected?

[Guest Kelly Igel]

When a Plan amends its definition of compensation, and/or adds a compensation exclusion (i.e., bonuses, overtime, or compensation earned before a participant's "entry date")...

Can these types of changes be made mid-plan year? Or, if the effect of these amendments is a reduction in the compensation that will be considered for that year, is that a reduction of an IRS protected benefit? Say this is for a 401(k) plan with a discretionary match and discretionary profit sharing made at year-end.

If any of the contributions were mandatory, would that have any bearing on the ability to amend the definition mid-plan year?

Does the presence of an "employed on the last day" requirement have any bearing on the ability to do this mid-plan year? (The impact of the definition of Compensation, however, extends beyond those provisions that can have a "last day" requirement...)

Thanks for your input...