If a Social Security Number (SSN) is marked “Not Valid for Employment,” it means the person has a restricted SSN or may have an ITIN instead. The IRS requires an SSN that is valid for work to claim certain credits, including the Earned Income Credit (EIC). If someone on your return has a restricted SSN, they are not eligible for EIC.
Checking this box tells the program to remove EIC from your return and helps ensure your taxes are filed correctly to avoid delays or IRS notices. Only check it if the SSN is restricted or not valid for employment—otherwise, leave it unchecked.