The IRS Automated Underreporter function (AUR) compares third-party information returns against what you reported on your tax return to identify discrepancies. The IRS describes the process as automated matching followed by tax examiner review, and it issues a CP2000 notice when the discrepancy remains after that review. AUR matching does not require a field auditor to open a traditional audit file. It uses third-party reporting and automation to force a fast decision: agree, dispute with documentation, or risk escalation into assessment, statutory deficiency procedures, and eventually collections. The IRS also treats AUR as a structured compliance pipeline, and the Internal Revenue Manual (IRM) contemplates transfers out of AUR into Examination or Criminal Tax Investigation in appropriate cases.
The Third-Party Data That Drives AUR Matches
AUR matches what you report against information the IRS receives from employers, banks, brokers, platforms, and other payers on Forms W-2, 1098, 1099, and related information returns. The cleanest way to see what the IRS likely matched is the Wage and Income Transcript. The IRS explains that this transcript shows data reported on information returns such as Forms W-2, the Form 1099 series, the Form 1098 series, and the Form 5498 series, and that state and local information is not included with the Form W-2 information. When you build a response posture, you should treat that transcript as the government’s baseline data set, then reconcile it to the positions you reported and the records you can actually produce.
Third-party reporting now reaches further than most taxpayers assume, and that scope drives the scrutiny. For example, payment cards generate Form 1099-K reporting with no dollar or transaction threshold when a taxpayer takes direct card payments through a processor. For payment apps and online marketplaces (TPSOs), the IRS has stated that the One Big Beautiful Bill retroactively reinstated the prior federal reporting threshold, so TPSOs generally do not have to file Form 1099-K unless gross reportable payments exceed $20,000 and the number of transactions exceeds 200. Even so, the IRS warns that platforms may still issue Form 1099-K for lower amounts and fewer transactions, and the taxpayer must still report taxable income whether or not a platform issues a form.
How AUR Correspondence Escalates When You Ignore It
AUR often starts with either CP2501 or CP2000, depending on the item and how the IRS processes the discrepancy. The IRS describes CP2000 as not a bill but a proposal to adjust income, payments, credits, and/or deductions, and explains that the notice shows what you reported, what the payer reported, and the proposed changes. The IRS also instructs taxpayers to complete the response form when included, state whether they agree or disagree, and include supporting documentation, and warns that interest accrues until payment is made and that penalties may apply.
The IRS builds pressure through deadlines and staged correspondence. In its CP2000 explainer materials, the IRS instructs taxpayers to reply and send supporting documentation within 30 days of the letter’s date, and to call the number on the notice if they cannot meet the deadline and need more time. If you do not reply or the IRS cannot resolve the discrepancy, the IRS may send another notice and then a bill. If the dispute persists or you do nothing, AUR can move into the statutory notice phase. The IRM states that when the taxpayer response does not resolve the issue, when no response occurs, or when the notice is undeliverable, the IRS issues a statutory notice of deficiency (CP3219A) in the AUR program. The IRS also states that CP3219A is not a bill or an audit, but it notifies you of a proposed change and explains how to challenge the decision in the U.S. Tax Court.
How to Dispute an AUR Mismatch Without Creating Criminal Tax Risk
Most AUR matters stay civil, but third-party mismatches often involve underreported income themes, and sloppy responses can create facts the government later frames as willful. You should treat the first response as a credibility document. You should not “explain first and document later.” You should reconcile the Wage and Income Transcript to the filed return, identify whether the issue is ownership, timing, duplication, or reporting location, and then support the position with objective records that a third party could verify. The IRS emphasizes that the CP2000 review centers on what you reported versus what payers reported, so you should expect the government to test your story against payer and processor records.
You should also understand the legal leverage and its limits. IRC § 6201(d) shifts the burden of production in court proceedings when a taxpayer reasonably disputes an item of income on an information return and fully cooperates, requiring the IRS to produce reasonable and probative information beyond the information return. That rule does not immunize you from AUR, but it reinforces a practical point: you should frame disputes as specific, reasonable, document-supported challenges rather than broad denials, and you should cooperate in a controlled way that does not create inconsistent statements.
If the mismatch touches cash receipts, payroll, nominee reporting, large repeated omissions, or records that do not reconcile cleanly, you should assume eggshell or reverse-eggshell risk until you prove otherwise. AUR can transfer cases to other IRS functions, including Examination or Criminal Investigation, and the IRM explicitly contemplates that transfer mechanism. You reduce criminal tax investigation risk by avoiding three categories of self-inflicted damage: submitting altered or fabricated documents, backfilling records that contradict third-party data, and giving explanations that you cannot later support with records. You should route sensitive factual development through counsel when the facts do not tolerate improvisation, because only counsel can provide attorney-client privilege and structure accountant involvement through a Kovel arrangement when you need confidential financial analysis to support legal strategy.
California state often follows through, increasing the cost of losing an AUR dispute. California requires taxpayers to report federal changes within 6 months of the final federal determination, and the FTB warns that it may keep the statute of limitations open if neither the taxpayer nor the IRS provides timely notification of the federal changes. If you operate in California state or you file California tax returns, you should treat federal AUR outcomes as state-exposure events, not as federal-only letters.
Contact the Tax Law Offices of David W. Klasing if you are worried about AUR matching and third-party data-driven scrutiny
Contact the Tax Law Offices of David W. Klasing if you received a CP2000 or related AUR correspondence and need an attorney-led, transaction-supported reconciliation that you can defend against payer and processor records and transcripts. AUR matching disputes often look “small” until they harden into assessments, trigger statutory deficiency procedures, or spill into California through required federal-change reporting. You should involve dual-licensed Tax Attorneys and CPAs when you need one team to control communications, preserve privilege, build a defensible factual record, and pursue damage control with the goal of keeping the matter civil whenever the facts allow.
Contact the dual-licensed Civil and Criminal Tax Attorneys & CPAs the Tax Law Offices of David W. Klasing if the mismatch involves repeated underreporting themes, platform reporting (including Form 1099-K), broker reporting, cash-intensive activity, payroll tax exposure, or any fact pattern that could support a criminal tax investigation narrative if you respond carelessly. Call the Tax Law Offices of David W. Klasing at 800-681-1295 or schedule a reduced-rate initial consultation through the firm’s online portal HERE.
