What of these tax forms allows an employer to claim an exemption from federal?

The tax form that allows an employer to claim an exemption from federal income tax withholding is the IRS Form W-4. Employees fill out this form to indicate their tax situation, including any exemptions they may qualify for, which the employer then uses to determine the amount of federal income tax to withhold from their paychecks. Additionally, non-profit organizations may use IRS Form 990 to claim tax-exempt status, but this pertains more to the organization's overall tax obligations rather than individual employee exemptions.