Is this about your personal tax return, not a business? These are pilot versions of the IRS identity-verification letters. Treat a 6330C like a 4883C (call the number on the letter) and a 6331C like a 5071C (verify at IRS.gov/VerifyReturn or call). The return and refund are held until you do. If you lost the letter, the IRS will send the standard version after you confirm your identity. The rest of this page goes deeper, from the side of the businesses that file 1099s; the parts on how the IRS handles the letter apply to you too.
What Letters 6330C and 6331C is
Two Taxpayer Protection Program letters "Issued on accounts as part of a TPP pilot." The manual tells assistors that for a 6330C "employees will use procedures for Letter 4883C" (telephone verification) and for a 6331C the procedures for Letter 5071C (online or telephone), and that "The pilot letter cannot be reissued"; a lost one is replaced by the corresponding standard letter (IRM 25.25.6.1.7, June 15, 2026). The return under the person's number is held until they verify that they filed it.
The deadline
None printed; the return and any refund wait for verification, and no account information is released while the issue is open. Up to nine weeks to post after verification.
What to do
Treat a 6330C as a 4883C: call the number on the letter with the letter and the returns. Treat a 6331C as a 5071C: verify at IRS.gov/VerifyReturn or call. If the letter is lost, the IRS issues a 4883C or 5071C in its place after you authenticate your identity. If you did not file the return, report that on the call.
Questions about Letters 6330C and 6331C
Who receives Letters 6330C and 6331C?
Individual taxpayer. Two Taxpayer Protection Program letters "Issued on accounts as part of a TPP pilot." The manual tells assistors that for a 6330C "employees will use procedures for Letter 4883C" (telephone verification) and for a 6331C…
What is the deadline on Letters 6330C and 6331C?
None printed; the return and any refund wait for verification, and no account information is released while the issue is open. Up to nine weeks to post after verification.
What should I do when Letters 6330C and 6331C arrives?
Treat a 6330C as a 4883C: call the number on the letter with the letter and the returns. Treat a 6331C as a 5071C: verify at IRS.gov/VerifyReturn or call. If the letter is lost, the IRS issues a 4883C or 5071C in its place after you authenticate your identity. If you did not file the return, report that on the call.
Is Letters 6330C and 6331C about my own income tax?
No. This decoder covers information reporting and withholding: the notices a payer, filer or payee sees because of Forms 1099, W-2, 945 and the TINs on them. Individual income-tax notices follow a different track.
Have a different notice? The IRS notice decoder lists all 83 in the order they tend to arrive.