Backup withholding: what a CP2100 notice requires of payers

An IRS notice numbered CP2100 or CP2100A tends to reach the accounts payable desk in the fall or the spring. With it comes a list of people and companies you paid, each flagged because the name and taxpayer identification number (TIN) on your Form 1099 is missing or doesn't match IRS records.

IRS instructions for the notice read as a list of tasks. You compare the list against your own vendor files and write to the payees whose information you reported exactly as they gave it. If those letters go unanswered, backup withholding on their next payments follows.

We see this notice treated as routine mail more often than it deserves. Its deadlines are counted in business days, and a payer that misses them can end up answering for tax that was supposed to come out of someone else's payment.

This article covers the federal rules only, from the payer's side, for payees with missing or incorrect TINs. It leaves out Oklahoma's own withholding rules, the deposit schedule for withheld amounts, penalty dollar figures, and the separate track for payees the IRS says underreported interest or dividends.

What backup withholding is, and why a CP2100 sets it in motion

The IRS describes it as "mandatory federal income tax withholding on reportable, non-payroll payments." In plain terms, a business that would normally pay a vendor in full holds back part of the payment and sends it to the IRS, where it counts toward the vendor's own income tax.

IRS Tax Topic 307 puts the figure plainly: the payer "must withhold at a flat 24% rate." The statute, 26 U.S.C. § 3406, doesn't print a number. It sets the tax by cross-reference to a rate in another Code section, which is why the IRS guidance is the easier place to confirm the current figure.

Tax Topic 307 says the rule can apply to most kinds of payments reported on Form 1099. For an Oklahoma operating company, the ones that come up are nonemployee compensation to contractors, rents, royalties, gross proceeds paid to an attorney, and interest or dividends.

Section 3406 lists four conditions that trigger the withholding, and the statute confines two of them to interest and dividend payments. The two that matter to most payers are simpler: the payee never furnished a TIN in the required manner, or the IRS has notified the payer that the TIN is incorrect.

That second condition is the CP2100's job. The IRS says its "B" program runs under section 3406(a)(1)(B) and Treasury Regulation 31.3406(d)-5.

CP2100 or CP2100A

The difference is volume. According to the IRS, a payer that filed 50 or more information returns with errors receives the CP2100, and a payer with fewer than 50 receives the CP2100A. Both carry the same information and instructions.

These notices go out twice a year, the IRS says, in October and the following April. The agency also suggests checking that the mailing address it has for your business is current, and it names Form 8822-B as the way to update one.

The walkthrough: what the payer does, in order

First, sort the list against your records

Publication 1281 is the IRS's manual for this process, and it starts with a comparison. Each listed account falls into one of two groups: TINs that are missing or obviously incorrect, and TINs that look valid but don't match the name in IRS records.

An obviously incorrect TIN, in the IRS's description, is one with fewer or more than nine digits or one that includes a letter.

For the mismatches, the first thing to settle is whether the list agrees with what the payee actually gave you. If your own files show a different name or number, because someone keyed it wrong or the payee updated it after you filed, the IRS says the only thing to do is correct or update your records. No "B" notice goes out.

Publication 1281 covers one more possibility, which is that the IRS misprinted your information. In that case it says to make a note in your records and take no action.

Either way, nothing goes back to the IRS. The agency's guidance says not to call or write to report that you've corrected your records.

Missing and obviously incorrect TINs

Here the rule is blunt. If backup withholding isn't already in place for that payee, the IRS says to begin it immediately and to keep withholding on payments until the payee supplies a TIN.

The payer also has to ask. IRS guidance calls for up to three requests for the TIN, an initial one and two annual follow-ups, and ties those requests to avoiding a penalty for filing an information return without a TIN.

The first "B" notice

When a payee appears on the list for the first time and your records match what the IRS printed, the payer sends what the IRS calls the First "B" Notice, along with a Form W-9. Form W-9 is the form on which a payee gives its name and TIN and certifies them under penalties of perjury.

Publication 1281 gives the payer 15 business days to send it, counted from the date of the CP2100 or CP2100A or the date the payer received it, "whichever is later."

If the payee returns a signed W-9, the payer has what it needs and doesn't backup withhold. One wrinkle surprises people: the publication doesn't require the W-9 to show a different name or number. If it comes back certifying the same combination the IRS flagged, the publication says to keep the form on file to show that the payee certified it.

Silence is the other outcome. The payer must then begin withholding on reportable payments to that payee no later than 30 business days after receiving the notice. A payer may start sooner, as early as the day after the notice arrives.

Stopping has its own clock. Once the certified W-9 arrives, the payer must stop withholding within 30 calendar days. Business days to start, calendar days to stop: in our experience that mismatch is where a calendar entry goes wrong.

The second "B" notice is different in kind

A payee listed a second time within three calendar years gets the Second "B" Notice, and this one goes out without a Form W-9. A fresh certification from the payee no longer cures the problem.

Instead, the payee has to bring proof from the agency that issued the number. For an individual using a Social Security number, the IRS says that means a copy of the Social Security card. For a business using an employer identification number, it means IRS Letter 147C, which verifies that the name and number are correct.

Until that validation reaches the payer, the payer can't stop withholding once it has begun.

Publication 1281 has rules for the edge cases too. A second CP2100 or CP2100A in the same calendar year as the first may be disregarded for that payee, and a third or later notice can generally be ignored if the earlier steps were completed and the name and TIN combination hasn't changed. A different combination is treated as a first notice.

All of this assumes somebody is keeping track. The publication requires payers to track listed accounts for three years after the date of the first notice, which in practice means a log that survives staff turnover.

Reporting what you withheld

Withheld amounts are reported on Form 945, the Annual Return of Withheld Federal Income Tax, and Publication 1281 tells payers to make the required deposits. The IRS notice page adds that Form 945 is filed under the same name and employer identification number used on the information returns.

The payment still has to be reported on the payee's Form 1099. The IRS says that is true even when the payment is below the amount that would normally require an information return, a point to keep in mind alongside the ordinary reporting threshold for Forms 1099.

A hypothetical with round numbers

Consider a hypothetical, with invented figures. An Oklahoma City fabrication shop pays an independent welding contractor $10,000 a month. The contractor shows up on the shop's CP2100A for the first time, and the W-9 in the shop's file matches the name and number the IRS printed.

The shop mails the First "B" Notice and a blank W-9 inside the 15-business-day window. No reply comes. On the first payment after the 30-business-day mark, the shop withholds 24% of $10,000, which is $2,400, and pays the contractor $7,600.

After three such payments, the shop has withheld $7,200 on $30,000 of invoices and paid out $22,800. It reports the $7,200 on Form 945 and shows it on the contractor's Form 1099.

Now run the same facts with the notice sitting in a drawer. The shop pays all $30,000. The $7,200 is still the amount the law required it to withhold, and the contractor already has the money it would have come from.

Where the payer's exposure sits

That last scenario is the part owners tend to miss. The statute puts the duty on the payer in so many words: "the payor shall deduct and withhold." It then treats payments subject to backup withholding, for purposes of the withholding chapter, "as if they were wages paid by an employer to an employee."

Wage withholding comes with a liability rule. Under 26 U.S.C. § 3403, the employer is liable for the tax required to be deducted and withheld. The instructions for Form W-9 requesters reprinted in Publication 1281 make the point in plainer words: if you don't collect backup withholding as required, "you may become liable for any uncollected amount."

The word "may" is doing real work there. Whether, and how much, a payer ends up owing when the payee reports the income and pays its own tax is a fact-specific question this article doesn't take up. The starting position, though, is that the exposure belongs to the payer and is measured by payments already made.

Penalties are a second, separate track. Publication 1281 refers to a Proposed Penalty Notice, numbered 972CG, as a different notice from the CP2100. The IRS's 2026 general instructions for information returns warn that a filer may be subject to a penalty for a missing or incorrect TIN, and they place the penalty for incorrect information returns under section 6721.

There is an honest counterweight: the rules give a payer who follows them something to stand on. Publication 1281 points to a companion publication on reducing or removing penalties for reasonable cause, and in our experience the dated copies of TIN requests and "B" notices are the first thing anyone asks to see. Section 3403 also says the employer, which is the position the wage treatment in section 3406 gives the payer, is not liable to any person for the amount of the payment, a provision that speaks to the vendor who objects to a short check.

Leaving a notice unanswered is a broader subject, covered in what happens when you ignore an IRS notice.

The payee's side of the letter

The payee gets no warning from the IRS. The agency's "B" program page poses the point directly, whether a payee will get notice from the IRS before the withholding starts, and answers no. The first a contractor or landlord hears of the problem is the payer's letter.

That makes the payer the messenger, and in our experience the messenger takes the heat. A long-time vendor who receives a form letter about withholding often reads it as an accusation.

It isn't one. The mismatch can have an innocent cause, and Publication 1281 names one: a name changed through marriage or divorce that was never reported to the Social Security Administration. The publication also says a sole proprietor must always furnish the individual's name and must not furnish only the business name.

Money withheld isn't a penalty either. Tax Topic 307 says a payee whose Form 1099 shows backup withholding reports it as federal income tax withheld on the return for the year the income was received. It works as a prepayment, much like the withholding on a paycheck.

When the payee is a partnership or S corporation

Here the credit doesn't stay where the cash was taken. Tax Topic 307 says backup withholding on a partnership or S corporation can be claimed only by the partners and shareholders, and that the amounts aren't refundable to the entity.

For a closely held company on the receiving end, that separates the pain from the remedy. The entity's operating account is short by the withheld amount, and the offsetting credit belongs to the owners. Owners who don't expect that can end up negotiating among themselves over cash nobody planned to move.

The cheaper fixes come before the notice

Every step above is harder than collecting a signed Form W-9 before the first payment goes out. A payer that holds a certified TIN from the start has made its first request and has a document to compare against the IRS's list.

Cheaper still is checking the number before filing. The IRS runs a TIN Matching program, and it says payers of most Forms 1099 can apply to use it to verify name and TIN combinations ahead of filing, interactively or in bulk.

Neither tool is permanent. A name that matched at onboarding can stop matching after a marriage or a divorce, so the list can still arrive at a careful company.

For Oklahoma companies that pay royalty owners, state-level withholding is its own subject, and we take it up in our article on Oklahoma withholding for nonresident royalty owners. Nothing in this piece speaks to Oklahoma's rules.

If a CP2100 or CP2100A is on your desk and you aren't sure which step you're on, a conversation now is usually less expensive than sorting out missed withholding later. You can reach us through the contact page or at our Oklahoma City office.

This article is general information about Oklahoma, Texas, and federal law, not legal advice, and it does not create an attorney-client relationship. Facts matter; talk to a lawyer about yours.