Employees complete Form W-4, “Employee’s Withholding Certificate,” to let you know how much federal income tax to pull from their paychecks. Most submissions are straightforward, but every so often you’ll run into something that gives you pause — an altered form, an odd attached statement, or a notice directly from the IRS. Knowing how to handle these situations correctly keeps your business compliant and ensures you don’t get pulled into an employee’s personal tax dispute.
SPOTTING AN INVALID FORM W-4
Employees are responsible for the accuracy of the information they provide on Form W-4, and they sign the form under penalties of perjury. As the employer, you generally do not need to verify whether their filing status, credits, deductions, or other adjustments are correct.
However, a Form W-4 is invalid if the employee:
- Alters the official form in any way,
- Deletes or crosses out the penalties-of-perjury declaration, or
- States outright that information on the form is false.
You must also reject any substitute form created by an employee. If your business develops its own electronic or paper substitute, it may be acceptable — but only if it meets all IRS requirements.
What to Do With an Invalid Submission
If an employee hands you an invalid Form W-4, explain that you cannot accept it and ask for a valid replacement. In most cases, you can keep withholding based on the last valid form you have on file until the new one arrives. If no valid form exists, withhold as if the employee selected “single or married filing separately” with no entries in Steps 2, 3, or 4.
Exemption Claims Are Not Automatically Invalid
A claim of exemption from withholding is not automatically a red flag. Starting with the 2026 Form W-4, employees use the exemption checkbox to make this claim. For 2026, an employee may generally claim exemption only if they had no federal income tax liability in 2025 and expect none in 2026. The responsibility for determining whether those conditions are met falls on the employee, not you.
RESPONDING TO IRS LOCK-IN LETTERS
You are not required to send Forms W-4 to the IRS on a routine basis. You only need to submit them when you receive a written IRS notice or specific published guidance directing you to do so.
The IRS reviews Forms W-2 and other records to flag employees whose withholding appears too low. If the IRS determines that an employee needs to have more tax withheld, it will send you a “lock-in letter.” This letter specifies the filing status and adjustments you must use going forward. Before the lock-in instructions kick in, the employee receives their own notice and a chance to dispute the determination directly with the IRS.
Honoring the Lock-In Letter
Once a lock-in letter is in effect, you must ignore any new Form W-4 that would drop withholding below the IRS-mandated amount. On the flip side, you must honor a new form that results in more withholding. If your business accepts W-4s electronically, your system should be set up to block employees subject to a lock-in letter from reducing their withholding beneath the locked-in amount.
If an employee disagrees with the lock-in determination, they must resolve it directly with the IRS. They can submit a new Form W-4 and supporting documents to the address listed in their IRS notice. Do not reduce withholding unless the IRS explicitly authorizes the change. Businesses that ignore lock-in instructions risk becoming liable for the additional tax that should have been withheld.
BUILDING CONSISTENT PAYROLL PROCEDURES
Your internal payroll procedures should clearly outline how Forms W-4 are submitted, reviewed, and retained. Train your payroll team to recognize altered or unauthorized forms, but do not ask them to judge whether an employee has calculated the “right” amount of withholding. That responsibility belongs to the employee — and, when necessary, the IRS.
For employees who have questions about completing Form W-4, direct them to the IRS Tax Withholding Estimator or suggest they speak with their personal tax advisor. Unless your business is specifically qualified and authorized to provide tax advice, avoid giving individualized guidance.
KNOW WHEN TO GET HELP
Unusual Forms W-4 and IRS lock-in letters can expose your business to real compliance risks if mishandled. We can walk you through the withholding rules, evaluate your current payroll procedures, and help you respond properly to invalid forms or IRS directives. Reach out today to protect your business from costly withholding errors.