Class code
A class code is the classification NCCI or your state bureau assigns to a category of work, like roofing, electrical, or general carpentry, for workers' compensation rating purposes. Your payroll is reported by class code, and each code carries its own expected loss rate, the baseline your actual claims get measured against when your EMR (experience modification rate) is calculated. Class codes matter because they change the comparison, not just the label. Payroll sitting under a class code that doesn't match the work it actually pays for, often because a code was assigned once years ago and never revisited as operations shifted, measures you against the wrong baseline entirely. A framing crew coded as general labor is a common version of this. Checking that every class code on your experience rating worksheet matches your current scope of work is one of the more overlooked corrections, since it changes the denominator every claim gets compared against rather than any single claim itself.
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Source
Is your mod right?
Most contractors have never had the worksheet compared to the loss runs and payroll behind it. See what your mod is costing you, or get on the list for a full verification.