When the IRS contacts your customers and vendors: Letter 3164, the 45-day wait, and the list you can demand

What counts as a third-party contact

The regulation's definition has five parts, and the manual repeats them: a communication that "is initiated by an IRS employee, is made with a person other than the taxpayer, is made with respect to the determination or collection of a tax liability of such taxpayer, discloses the taxpayer's identity, and discloses the association of the IRS employee with the IRS" (IRM 25.27.1.2, May 6, 2026, quoting 26 CFR 301.7602-2). All five have to be present. A database search is not a contact; a call to a government office for your address is not; a call to your contractor asking whether you paid him what the 1099 says is.

The manual's own list of what is a contact includes "contacts made with employees of the taxpayer who are questioned outside the scope of their normal employment when the taxpayer is a business," a follow-up solicitation after a third party called the IRS first, and contacts about "the taxpayer's business with the government office contacted, such as the taxpayer's contracts with or employment by the office" (IRM 25.27.1.2). Information a third party volunteers is not a contact until the IRS calls back for more.

The notice: Letter 3164 and the 45 days

"It is the IRS's practice to obtain information relating to a liability or collectibility determination directly from the taxpayer whenever possible" (IRM 25.27.1.3). When it goes elsewhere, the Taxpayer First Act rewrote the notice rule in 2019. The IRS "must have an intent, at the time such notice is issued, to contact third parties," "must specify in the notice the time period, not to exceed one year, within which the IRS intends to make the third-party contact(s)," and "must send the notice at least 45 days before the first contact with a third party" (IRM 25.27.1.3, May 6, 2026). "A notice shall not be issued unless there is an intent to contact third parties at the time such notice is issued," which ended the old practice of a blanket warning in every case. "Effective August 15, 2019, Publication 1 no longer satisfies the advance notice requirement" (IRM 25.27.1.3.1).

The notice is Letter 3164, in "over twenty versions" for different functions, hand delivered or mailed to the last known address; for a joint return each spouse gets one. "Employees may not contact a third party until the 46th day following the date of the notice" (IRM 25.27.1.3.1). If the IRS wants to keep contacting people past the one-year window it has to send a refresher, and the manual, incorporating a January 2025 interim guidance memo, tells employees to send it "no less than 46 days before the expiration of the current TPC one year period" or face "another 45-day waiting period." If a new address turns up after the letter went out, a copy marked "copy" goes to the new address, and the 46 days still run from the original (IRM 4.11.57.4.1, Oct. 5, 2022).

Who gets the letter follows the return. For a partnership or S corporation examined at the entity level, the entity; if the IRS is contacting someone about a transaction that affects only specific partners, those partners; and "if an employee or officer of a corporation will be questioned about an issue on the shareholder's individual tax return, the shareholder must receive advance notice" (IRM 4.11.57.4.1).

How a contact is made and recorded

In examination, "a third-party contact (TPC) is made when the taxpayer is unable or unwilling to provide the necessary information or when the examiner needs to verify information provided. The examiner should generally request the information on a Form 4564, Information Document Request, before making a TPC. Examiners must document the case file to support the need to verify information already provided by the taxpayer" (IRM 4.11.57.2, Oct. 5, 2022). "Generally, third parties should not be contacted prior to an examination." The 2025 revision added the mechanics: a third party at a residential address gets a letter (Letter 1995) first; at a business address, a letter or an unannounced visit; a non-response is followed by phone (IRM 4.11.57.6, Feb. 26, 2025).

Each contact is recorded on Form 12175, "a separate Form 12175 for each third party on each day a contact is made, even if it is with the same person," sent to a coordinator who maintains the database the list is drawn from (IRM 25.27.1.4, May 6, 2026). A contact made by mail is held until the third party has had time to raise a fear of reprisal. The examiner is told to make a reprisal determination "on a contact-by-contact basis (no blanket determinations)" (IRM 25.27.1.3), and "a potentially dangerous taxpayer (PDT) indicator alone is not a sufficient basis" for one (IRM 25.27.1.3.4).

Getting the list: Letter 3173

"A taxpayer can request a list of TPCs at any time. The request can be made either orally or in writing" (IRM 25.27.1.5, May 6, 2026), and "employees are responsible for ensuring that taxpayers understand their rights to receive post third-party contact reports." The request must give the name, address, TIN and tax periods; cover one taxpayer (joint requests are returned); ask for contacts already made, not future ones; and come "no less than 90 days from a previous request." An incomplete request comes back with Letter 6415. The coordinator answers with Letter 3173, listing "all TPCs other than those excluded due to fear of reprisal or other statutory basis" made since January 18, 1999 or since the last list.

What the list will not show is as useful as what it will. It omits contacts covered by a reprisal determination, contacts the taxpayer was notified of under another statute (summons, CDP), government offices, and anyone the IRS treats as a confidential informant, which under IRM 25.2.2.10 includes a whistleblower. A list with nothing on it is not proof that no one talked to the IRS.

The exceptions

IRC 7602(c)(3) and 26 CFR 301.7602-2(f) carry the exceptions, and the IRS reads them as seven (IRM 4.11.57.5, Oct. 5, 2022):

When the IRS contacts you about a payee

The program works in both directions. When an examiner working a contractor's return calls you to confirm what you paid, you are the third party; the contractor should have received a Letter 3164 at least 45 days earlier, your name is recorded on Form 12175, and you will be told that it goes on a list the contractor can request. If you have reason to fear the contractor's reaction, say so: the reprisal exception removes your name from the list and from the advance notice, and the manual tells the employee to keep anything identifying you "in a confidential envelope and clearly marked" (IRM 25.27.1.3.3). The page on IRS inquiries about a payee covers what the IRS has already looked at before it calls, and the payee's-audit page the rules that make the call necessary.

Two payee-side contacts fall outside the program. The automated underreporter's Letter 2625-C to a payer goes out only after the payee has signed a consent (Form 2624), so it is an authorized contact; and a whistleblower is never a third party. A payer that receives a 2625-C is not being audited and is not on anyone's Letter 3173.

What it means for a payer

• Read the Letter 3164 for its window. It names the tax periods and an end date no more than a year out. Contacts outside the window, or before day 46, are contacts the examiner was not permitted to make; raise it with the manager or in Appeals, where the technical reviewers check "whether Examination employees observed the advance general notice requirements" (IRM 4.8.8.18, cited at 25.27.1.1.7).
• Answer the IDR, and you narrow the contacts. The manual conditions a third-party contact on your being "unable or unwilling to provide the necessary information" or on the examiner's need to verify. Complete W-9s, TIN matching results and payment records answer the questions the examiner would otherwise put to your contractors.
• Ask for the list, in writing, with the four items. Name, address, TIN, periods; one entity per request; no more often than every 90 days. Keep the Letter 3173 with the audit file.
• Authorize contacts yourself when it helps. Form 12180 lets you name the vendors or customers the examiner may call, which skips the 45-day wait and keeps the contacts to the ones you chose. A representative needs line 5a of the 2848 checked to do it for you.
• Tell your people what the call is. A vendor who gets Letter 1995 will see your name in it. A short note that the IRS may verify payments, and that cooperating is the quickest end to it, prevents the panicked call that becomes a second contact.

Questions people ask