June 24, 2019 The IRS issues Backup Withholding CP2100 or CP2100A Notices to payers. These notices let payers know backup withholding may need to begin for some taxpayers. Backup withholding begins if a taxpayer identification number is missing or for incorrect name/TIN combinations. Payers who receive these notifications should compare the information in the notice with their records. For missing TINs: Determine if backup withholding is already set up, if not, begin immediately. For incorrect TINs: Compare the accounts on the listing. If they agree notify the taxpayer. If not, correct or update. Payers don’t need to send corrections made to the IRS and shouldn’t respond to the notice. For more information, see Publication 1281 PDF.