Quick orientation

An IRS letter or notice is an official, written communication from the Internal Revenue Service about your tax account. Letters use short codes (series) such as “CP” or “LT” plus numbers to identify the topic and urgency. Decoding those codes quickly helps you avoid missed deadlines, unnecessary payments, or collection actions. (See the IRS page “Understanding Your IRS Notice or Letter” for examples and official guidance: https://www.irs.gov/individuals/understanding-your-tax-notice-or-letter.)

This guide explains how the series system works, what common codes mean, step-by-step response actions, and practical tips I use in my practice when helping clients reply to IRS correspondence.

How IRS letters are structured and what the codes mean

IRS letters follow a consistent format: a header with the notice name/code, a short explanation of the issue, what the IRS changed or proposes to change, and the action the taxpayer should take (pay, submit documents, or call). Common prefixes include:

  • CP (Computer Paragraph) — routine account notices (balance due, proposed changes, refund status). CP letters are often automated and include CP14 (balance due) and CP2000 (proposed change based on third-party reporting).
  • LT/LTR — collection or levy-related notices that may escalate to wage garnishment or bank levies (for example, LT11 is Notice of Intent to Levy).
  • Letter series numbers (3000–3999, 6000 etc.) — special-purpose letters (discovery, identity verification, or lien notices). Specific numbering varies by program.

The full code (prefix + number) tells you the underlying action and typical next steps. For instance, a CP2000 is a proposed adjustment; it is not an audit summons but does require a specific response if you disagree. (See IRS CP2000 resources: https://www.irs.gov/individuals/responding-to-a-cp2000-notice.)

Common IRS letters you will likely encounter

Below are everyday examples and the usual taxpayer response:

  • CP14 / Notice of Balance Due — A reminder that the IRS shows unpaid tax. Typical response: review your records for payments, pay or set up a payment plan, or contact the IRS if the balance is incorrect. (Internal resource: https://finhelp.io/glossary/irs-notice-cp14-balance-due/)
  • CP2000 / Proposed Adjustment — The IRS believes income, payments, or credits on your return do not match third-party reports (W-2, 1099). Typical response: agree and pay, or submit supporting documents to dispute. See our detailed how-to: https://finhelp.io/glossary/responding-to-a-cp2000-notice-steps-to-take/
  • CP3219A / Statutory Notice of Deficiency — A formal notice that can lead to IRS assessment if not timely contested; typically starts the process for a deficiency and explains appeal rights.
  • LT11 / Notice of Intent to Levy — A serious collection letter that explains your right to a Collection Due Process hearing if you request timely.
  • CP501 / Final reminder for unpaid taxes — Often follows earlier notices and may precede enforced collection.

These are representative examples; the IRS issues scores of specialized letters. If you need a quick decoder, see our quick reference: Interpreting IRS letter codes and the IRS’s official guidance (https://www.irs.gov/).

First 5 actions to take when you receive an IRS letter

  1. Pause and verify: Don’t assume the worst. Confirm the letter is legitimate (see steps below) before sharing personal data.
  2. Read the entire notice: Identify the code, the period or tax year affected, the proposed change or amount due, and the deadline.
  3. Check your records: Compare the IRS’s figures against your returns, W-2s, 1099s, and payment history.
  4. Respond exactly as requested: If the IRS asks for documents, send copies (not originals), include the notice copy and a clear cover letter, and follow the address or online link provided.
  5. Record and calendar: Log the notice, document what you sent, and calendar the deadline and any follow-up dates.

These steps keep your response organized and defensible if the case escalates later.

How to verify a letter is real (and avoid scams)

Scammers send fake IRS notices to steal money or identity. Confirm legitimacy by:

  • Checking the sender: Legitimate IRS mail comes from the U.S. Postal Service and will include an official IRS letterhead and contact phone numbers. The IRS will not initiate contact by email, text, or social media to demand immediate payment. (See IRS guidance on scams: https://www.irs.gov/newsroom/tax-scams-consumer-alerts.)
  • Calling the IRS using a verified number: The IRS main phone is listed on irs.gov; do not call numbers printed on a suspicious notice without verifying them.
  • Using our verification checklist: https://finhelp.io/glossary/how-to-verify-if-an-irs-letter-is-legitimate/ — it lists red flags and steps to confirm authenticity.

If you suspect identity theft, use the IRS identity protection pages and FTC resources for next steps. (See IRS Identity Theft Protection: https://www.irs.gov/identity-theft-fraud-scams/identity-theft-protection)

Responding: how to dispute, agree, or request more time

  • Dispute a proposed change: Send a written response explaining the disagreement, attach supporting documentation (W-2s, 1099s, bank statements), and use certified mail or the IRS online response channel if the notice permits.
  • Agree and pay: If the adjustment is correct, pay by the due date or apply for an installment agreement to avoid liens or levies. The IRS provides online payment options and installment agreement guidance on IRS.gov.
  • Request more time: If you need time to gather records or seek professional help, request additional time in writing. For collection notices that trigger levy actions, request a Collection Due Process hearing (see IRS Collection Due Process procedures).

For CP2000 notices specifically, follow the instructions in the notice. We have a step-by-step checklist for CP2000 responses at https://finhelp.io/glossary/responding-to-a-cp2000-notice-steps-to-take/ that many readers find helpful.

Payment and relief options

If you owe tax the IRS expects payment, options include:

  • Pay in full: Fastest way to stop interest and penalty accrual.
  • Installment agreement: Apply online or by phone to spread payments over months/years.
  • Offer in Compromise: A settlement for taxpayers who can’t pay full liability; strict eligibility rules apply.
  • Penalty abatement: If you have reasonable cause (e.g., serious illness), you may request penalty relief.

Use official IRS tools and forms (installment agreements and Offer in Compromise pages on IRS.gov) and consult a tax professional for complex cases.

Timelines, deadlines, and consequences of inaction

Deadlines matter. Some notices give you 30 days to respond; others start statutory deadlines for assessments or appeals. Ignoring a notice typically leads to interest, penalties, and potential enforced collection (levy or lien). Our timeline primer explains common notice deadlines and prioritization: https://finhelp.io/glossary/a-simple-guide-to-irs-letter-timelines-and-deadlines/.

When to hire a tax pro or attorney

Engage a credentialed tax pro if:

  • The letter threatens collection (levy, lien, or seizure).
  • The notice alleges large additional tax liability or fraud.
  • You need to request an Offer in Compromise or appeal a statutory notice.

In my practice, early professional involvement usually lowers taxpayer stress and reduces the risk of procedural mistakes. A tax pro can draft persuasive cover letters, prepare documentation, and negotiate payment terms.

Recordkeeping and follow‑up best practices

  • Keep copies of every notice and the documents you send back.
  • Use certified mail or trackable courier services when mailing proofs.
  • Maintain a single case file per notice and log all calls (name, badge number, date, time, and a brief note).

Good records make appeals and future disputes far easier.

Common mistakes to avoid

  • Waiting to open mail from the IRS.
  • Sending original documents instead of copies.
  • Calling unverified numbers on a suspicious notice.
  • Paying without verifying the correctness of the IRS math or claims.

Real-world examples (short)

  • Client A received a CP2000 claiming underreported freelance income. We produced 1099s and bank receipts; the IRS adjusted their account with no additional tax due.
  • Client B ignored an LT11 and later faced a bank levy. A timely response requesting a Collection Due Process hearing could have prevented the levy.

Final checklist (what to do right now)

  1. Verify the notice is genuine. 2. Read for the code, tax year, and deadline. 3. Match IRS figures to your records. 4. Respond with documentation or payment options. 5. Get help when the notice threatens collection or large liabilities.

Professional disclaimer: This article is educational and does not replace personalized tax or legal advice. For guidance tailored to your situation, consult a licensed tax professional or attorney.

Sources and further reading

If you want a printable checklist or templates for responses, our site has downloadable examples and sample cover letters to speed your reply.