TurboTax is asking about an Employer ID number (EIN) because you have Schedule H attached to your return. Schedule H is used to calculate household employees employment taxes. If you have household employees, you will need an EIN to file Schedule H.
For more information, refer to the TurboTax article What Is Schedule H: Household Employment Taxes and IRS FAQ About Schedule H (Form 1040), Household Employment Taxes.
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