The clearest signs the IRS is investigating you are a notice arriving by certified mail with a letter number in the upper right corner, an agent contacting you to schedule a meeting, people in your financial life reporting that the agency has reached out to them, or specific transaction codes showing up on your tax transcript. Which of these you see, and in what order, tells you whether the review is a routine civil audit or something more serious. Learning to read the signals early gives you time to pull records together, get representation, and avoid the mistakes people make when they either ignore the mail or say too much to the wrong agent.
The Mail Comes First
The IRS makes first contact by mail through the U.S. Postal Service.1Internal Revenue Service. How to Know It’s the IRS Every legitimate notice carries a specific letter or notice number in the upper right corner of the first page. You can look that number up on the IRS website to see what the letter is about and what response it requires.2Internal Revenue Service. Understanding Your IRS Notice or Letter The IRS and its authorized collection agencies will never demand payment through gift cards, prepaid debit cards, or cryptocurrency; any letter making those demands is a scam.3Internal Revenue Service. Ways to Tell if the IRS Is Reaching Out or if It’s a Scammer
The CP2000
The most common opening letter is the CP2000, generated by the IRS Automated Underreporter program. The system compares income on your return against W-2s, 1099s, and similar forms filed by employers, banks, and other payers. When it spots a mismatch, an examiner reviews the discrepancy and sends you a CP2000 proposing an adjustment.4Internal Revenue Service. Topic No. 652, Notice of Underreported Income – CP2000 It is not a bill and not necessarily an accusation. Sometimes the IRS data is simply incomplete, as when you sold stock at a loss but the brokerage only reported the sale price. It does mean someone at the agency is looking at your return.
You have 30 days from the date on the notice to respond, or 60 days if you live outside the United States.4Internal Revenue Service. Topic No. 652, Notice of Underreported Income – CP2000 If you agree, you sign and pay the difference. If you disagree, you send documentation. Let the deadline pass without responding and the IRS will assess the additional tax it proposed, eventually issuing a Statutory Notice of Deficiency, which starts a 90-day clock to petition the Tax Court before the agency can collect.5Taxpayer Advocate Service. Notice CP 2000
Escalation Letters
Letter 3176C is more serious. The IRS sends it when it determines a return is frivolous, meaning the return either lacks enough information to assess its accuracy or takes a legal position the IRS has flagged as having no basis in law. If you don’t correct the filing within 30 days, the agency assesses a $5,000 civil penalty under Section 6702 of the Internal Revenue Code, and the penalty applies separately to each frivolous submission.6Internal Revenue Service. Understanding Your Letter 3176C7Office of the Law Revision Counsel. 26 U.S. Code 6702 – Frivolous Tax Submissions
Pattern matters. A single CP2000 may be a data-matching hiccup. A CP2000 followed by additional correspondence requesting records or scheduling a meeting means the agency is digging deeper into specific items on that return.
Who Shows Up Tells You What Kind of Investigation It Is
A letter is one thing. An agent showing up is another. The type of agent reveals whether the IRS is running a routine civil audit or building a criminal case.
Revenue Agents Handle Civil Audits
Revenue Agents verify reported income, deductions, and credits. In a field audit, the agent works at your home, business, or your accountant’s office, and the IRS contacts you by mail first to schedule the appointment and tell you what to prepare.8Internal Revenue Service. IRS Audits1Internal Revenue Service. How to Know It’s the IRS Expect requests for receipts, canceled checks, bank statements, loan agreements, travel logs, and legal documents tied to your deductions.9Internal Revenue Service. IRS Audits: Records We Might Request
The goal is calculating the correct tax liability. The worst outcome is usually additional tax, interest, and accuracy-related penalties. If a Revenue Agent uncovers something that looks like deliberate fraud during a civil audit, the case can be referred to the Criminal Investigation Division.
Special Agents Mean a Criminal Case
Special Agents from the IRS Criminal Investigation (CI) Division are a different situation entirely. They are federal law enforcement officers who carry official credentials and may arrive unannounced at your home or workplace. Their job is not to calculate what you owe. It is to gather evidence for a potential criminal prosecution for offenses like tax evasion or filing false returns.
The most reliable indicator that a visit is criminal rather than civil is that two agents show up together. IRS Criminal Investigation procedure calls for at least two investigating officers at every interview with a subject, so that one can serve as a witness to what is said.10Internal Revenue Service. 9.4.5 Interviews If two agents appear at your door without a prior appointment, assume the conversation could produce evidence used against you in court. Do not answer substantive questions. Tell the agents you want to speak with an attorney and end the conversation. You are not required to let them inside or to provide a statement, and anything you say can be used to build the case.
When the IRS Starts Contacting Other People
When the IRS begins contacting people in your financial orbit, the investigation has moved well past your tax return. Federal law requires the agency to notify you before reaching out to third parties about your tax liability. The notice must arrive at least 45 days before the contact period begins.11Office of the Law Revision Counsel. 26 USC 7602 – Examination of Books and Witnesses You will typically receive Letter 3164, which says the IRS plans to contact outside sources like your bank, employer, or business associates, and specifies the time period during which those contacts will happen.12Internal Revenue Service. Understanding Your Letter 3164
If your bank tells you it received a summons for your account records, the investigation is well underway. The IRS can demand copies of deposit records, checks, and statements covering specific periods. When a third-party summons is served, the IRS must notify you within three days, and you cannot be forced to comply until at least 23 days have passed, giving you time to file a motion to block the summons if you have grounds.13Office of the Law Revision Counsel. 26 U.S. Code 7609 – Special Procedures for Third-Party Summonses
Hearing from a banker, vendor, business partner, or colleague that the IRS has been asking questions is one of the clearest signs the agency considers your case worth serious resources.
What Your Tax Transcript Can Tell You
You do not have to wait for a letter or a knock. IRS tax transcripts contain internal processing codes that can reveal whether your return has been flagged. You can access them through your Individual Online Account at IRS.gov. The Record of Account Transcript is the most complete version, combining your original return data with all subsequent changes.14Internal Revenue Service. Transcript Types for Individuals and Ways to Order Them
Transaction Code 420: Examination Started
TC 420 appears in the transaction history when a return has been selected for examination. It means a Revenue Agent has been assigned and normal processing has paused. The code can appear before you receive any letter, so checking your transcript periodically is one way to get ahead of the notification.
Transaction Code 810: Refund Freeze
TC 810 shows up when the IRS places a hold on your refund pending a compliance review. Depending on the responsibility code attached to it, the freeze could relate to identity theft screening, potential fraud, or review of specific credits like the Earned Income Tax Credit.15Internal Revenue Service. 21.5.6 Freeze Codes If you filed and your expected refund never arrived, pulling your transcript and looking for a TC 810 can tell you whether the delay is processing backlog or an active hold.
Transaction Code 421: Examination Closed
TC 421 indicates that an examination has been closed.16Internal Revenue Service. Transcripts in Lieu of Estate Tax Closing Letters If you previously saw TC 420 on your transcript and later see TC 421 appear, the audit is finished. The absence of TC 421 after a TC 420 means the review is still open.
How Long the IRS Has to Come After You
The IRS cannot investigate indefinitely in most cases. Federal law imposes time limits, and those limits stretch significantly when fraud is involved.
- Three years is the standard window. The IRS generally must assess additional tax within three years after your return was filed or due, whichever is later.17Office of the Law Revision Counsel. 26 U.S. Code 6501 – Limitations on Assessment and Collection
- Six years applies if you omitted more than 25 percent of your gross income from your return.18Internal Revenue Service. Time IRS Can Assess Tax
- There is no time limit if you filed a fraudulent return with intent to evade tax, or if you never filed at all.17Office of the Law Revision Counsel. 26 U.S. Code 6501 – Limitations on Assessment and Collection
Criminal prosecution has its own clock. The general limitation period for criminal tax offenses is three years from when the offense was committed, but for tax evasion and fraud against the United States, the government has six years to bring an indictment.19Office of the Law Revision Counsel. 26 U.S. Code 6531 – Periods of Limitation on Criminal Prosecutions If three or four years have passed since the return in question and you have heard nothing, the window is closing. If you never filed, or knowingly falsified a return, the clock never starts.
What to Do When You See the Signs
You can authorize an attorney, CPA, or enrolled agent to represent you before the IRS at every stage. A Power of Attorney filed on Form 2848 lets your representative argue facts, apply the law, negotiate, and sign documents on your behalf.20Internal Revenue Service. Power of Attorney and Other Authorizations In most situations, if you are in the middle of an interview with the IRS and want to consult a representative, the agency must stop the interview and give you time to do so.21Internal Revenue Service. Taxpayer Bill of Rights 9 – The Right to Retain Representation
If the inquiry has a criminal dimension, the stakes change fundamentally. Tax evasion carries up to five years in prison. Filing a false return carries up to three years. In a criminal investigation, you have the right to remain silent and to have an attorney present before answering questions. This applies whether Special Agents come to your home, your office, or ask you to come to theirs. People who cooperate fully with CI agents before consulting a lawyer frequently provide the statements that become the centerpiece of the prosecution.
Regardless of whether the investigation is civil or criminal, gather every document related to the tax years in question: returns, W-2s, 1099s, bank statements, receipts, and any records supporting deductions you claimed. Do not destroy, alter, or hide anything. Obstruction carries its own criminal penalties. Keep copies of every notice the IRS sends and every response you mail back. If you hire a representative, give them the full picture, including the facts that worry you. Attorney-client privilege protects those conversations, but only if you are honest with your lawyer.