IRS Letter About an Unfiled Business Return?

The short answer: A CP259, or the final reminder CP518B, means the IRS has no record of a business return it expects from your company’s EIN. The way to answer it is to file every return the letter lists or, if the company isn’t required to file one, to explain why on the Response form that came with it. Ignoring it lets penalties and interest keep growing, and the IRS can make a return for the company from its own information.

Which IRS letters mean a business return is missing?

For a corporation, look for two notice numbers, the CP259 and the CP518B, which both deal with business returns. The notice number is printed in the right corner of the letter.

CP259 is the first request. It says the IRS shows the company is required to file a return for the tax periods listed but hasn’t. It can be about the corporation’s income tax return or a payroll return such as Form 941 or Form 940, and the IRS mails a separate one for each form and period it shows as delinquent.
CP518B is the final reminder: the IRS still has no record of the returns. It asks for a signed paper return with all required schedules, sent with the completed Response form. The form is also where the company explains why it’s filing late, why it believes no return is due, or that it filed under a different name or EIN.

Some past-due-return notices, such as the CP59, are about personal returns instead. If your letter carries a different number, look it up on irs.gov before you act.

What is the letter asking you to do?

It’s asking for the return itself, for each form and period printed on it. There are three ways to answer:

File the return. The CP259 page says to file the required business return immediately, either electronically through your e-file provider, if the return is eligible for e-file, or on paper, with all required schedules. A CP518B asks for a signed paper return, sent with the Response form.
Tell the IRS it was already filed. If the company filed within the last four weeks under the same name and EIN shown on the notice, both notice pages say you may disregard it. If it was filed longer ago, or under a different name or EIN, the CP518B page says to explain that on the Response form.
Explain why no return is due. The Response form is also where you tell the IRS you don’t believe the company has to file for that period.

Be careful with the third option. The CP259 page says that a business with no employees or business activity during a period isn’t required to file for it, though it still has to respond. Don’t read that as a pass on the income tax return: the Form 1120 instructions say all domestic corporations must file whether or not they have taxable income, and an S corporation files Form 1120-S for as long as its election remains in effect. A quiet year usually still needs a return.

Is there a deadline?

Treat it as now. The irs.gov pages for these two notices don’t give a set number of days: the CP259 asks you to file immediately, and the CP518B is the final reminder. The IRS’s general guidance is that when a letter asks you to respond, you act by the due date, so if yours prints a date, that date governs.

If several years of books need rebuilding, the returns may not be ready by then. Don’t let the date pass in silence: the notice says how to reach the IRS. An officer of the company can make that contact, or an authorized representative can make it for the company.

What happens if you ignore it?

Penalties keep adding up. A C corporation’s late-filing penalty is 5% of the unpaid tax for each month or part of a month, up to 25%. For returns due in 2026, a return more than 60 days late carries a minimum of the smaller of the tax due or $525. The CP518B page adds that penalty and interest can continue to accrue.
S corporations pay per shareholder. An S corporation owes $255 per shareholder for each month late, up to 12 months, for a return required to be filed in 2026, even when no tax is due. Both amounts are adjusted for inflation, so a return that was due in an earlier year uses the amount set for that year. What a late 1120-S costs works through the S corporation figures.
The IRS can make the return for you. The CP518B says the IRS may determine your tax for you. Federal law (26 U.S.C. 6020(b)) lets it prepare a return from its own knowledge and whatever information it can obtain, and that return stands as valid unless it’s shown to be wrong. The IRS says it’s still in your best interest to file your own return even after it files one, so the company can claim all the deductions and credits it’s entitled to.
The clock doesn’t start until the company files. Once a return is filed, the IRS generally has three years to assess more tax. With no return, there’s no time limit, and a return the IRS makes itself doesn’t start the clock (26 U.S.C. 6501).
Unpaid tax moves toward collection. If assessed tax isn’t paid, the letters change. A CP504B is a notice of intent to levy, and it asks for payment, or a call, no later than 30 days from the date of the notice. An LT11 or Letter 1058 says the IRS intends to seize property or rights to property. Read the date on each of these letters. Refunds for other years may also be held up while a return is missing.

How do you respond by filing?

List what’s being asked for. Lay every letter out and write down each form and period. Because the IRS sends one notice per form and period, the letters together make a good first list, though not always a complete one. How to find every unfiled business return covers checking the rest.
Rebuild the books for each year. A return is only as reliable as the reconciled books behind it.
Prepare every listed return, with all schedules. For income tax, that’s Form 1120 for a C corporation, or Form 1120-S with a Schedule K-1 for each shareholder for an S corporation, plus any payroll returns (Form 941 or 940) the letters list.
Send it the way the notice asks. For a CP518B, that means a signed paper return with the completed Response form, in the envelope provided. Keep a copy of everything and the date you mailed it.
Pay what you can. Filing stops the late-filing penalty from growing. The late-payment penalty and interest keep running on any balance until it’s paid in full, even under a payment plan, so pay what you can when you file and ask for a payment plan for the rest.
Then look at the penalties. Penalty relief can be requested by you or an authorized representative, and it’s never certain. First-time abatement needs a clean three prior years: the same type of return filed on time, and no penalties other than any later removed for reasonable cause or an IRS error. For a company several years behind, that usually means it can cover only the first late year.
Check for the automatic exemption. For 2025 and later returns, including Forms 1120 and 1120-S, the IRS now applies an Automatic Exemption from Penalty, without a request, when the same return was filed and paid on time for the three prior years. Otherwise the question is reasonable cause.

When do you need an attorney, a CPA or an enrolled agent?

Not to answer the letter. The company can file the missing returns and send back the Response form without appointing a representative. Representation comes in when an outside professional has to deal with the IRS for the company, which takes a signed Form 2848, the power of attorney form. That’s also the route if you’d rather an outside professional spoke to the IRS for the company.

If your company needs a professional to represent it before the IRS, that’s the job of an attorney, a CPA or an enrolled agent. We’ll tell you on the call if your situation needs one and arrange it; it may be a separate engagement.

These are signs the situation has moved past a request for a missing return:

the letter is about an examination (an audit), not a missing return
a CP504B, an LT11 or a Letter 1058 has arrived, or the IRS has filed a lien or levied an account
the IRS has already made a return for the company and assessed tax you disagree with

If the returns were left unfiled on purpose, or you’re worried about how the IRS will view the missing years, speak to a tax attorney before anything is filed.

Cayde rebuilds the books and gets the returns a letter asks for filed, at a fixed price in writing first. IRS audits, levies, liens and Offers in Compromise are outside what Cayde handles. See how Cayde handles IRS letters.

Quick answers

Why did the company get several CP259 letters at once?

The IRS mails a separate notice for each form and tax period it shows as delinquent. Each one needs an answer: a filed return or a completed Response form.

The letter asks for Form 1120, but the company is an S corporation. Why?

A company files Form 1120-S only if it elected S corporation status on Form 2553, the IRS accepted the election, and the election is still in effect. A letter asking for Form 1120 can mean the IRS has no accepted election on file for those years, and that needs sorting out before the returns are filed.

How can you tell the letter is really from the IRS?

The IRS normally makes first contact by mail sent through the U.S. Postal Service. Look the notice number up on irs.gov and compare. By the IRS’s own description, a phone call, email or text that rushes you, threatens you or demands payment now isn’t from the IRS.

Does a CP259 mean the company is being audited?

No. A CP259 or CP518B asks for a return the IRS has no record of. An audit is a separate review of the books and records behind what a return reports. The IRS says it notifies you of an audit by mail and won’t start one by phone. An audit is one of the situations where the company may need an attorney, a CPA or an enrolled agent.

Sources

General information, not advice for your situation. Updated October 31, 2026.

The IRS sent a letter about a business return you never filed. What now?