Most employee Form W-4 submissions are straightforward, but occasionally an employer may receive a form that appears altered, incomplete or otherwise invalid. In other cases, the IRS may issue a lock-in letter requiring a specific amount of federal income tax withholding.
Understanding how to handle these situations can help your business remain compliant with IRS requirements while avoiding unnecessary involvement in an employee’s personal tax matters.
Recognizing an Invalid Form W-4
Employees are responsible for the information they provide on Form W-4, Employee’s Withholding Certificate, and they sign the form under penalties of perjury. Employers generally are not responsible for verifying whether an employee’s filing status, deductions or tax credits are accurate.
However, a Form W-4 is considered invalid if an employee:
- Alters the official IRS form
- Removes or crosses out the penalties-of-perjury statement
- Indicates the information provided is false
Likewise, employers shouldn’t accept substitute Forms W-4 created by employees. Employer-developed electronic or substitute forms may be acceptable if they comply with IRS requirements.
What Employers Should Do
If you receive an invalid Form W-4:
- Explain why the form can’t be accepted.
- Request that the employee submit a valid replacement.
- Continue using the most recent valid Form W-4 on file until a new one is received.
If no valid Form W-4 exists, withhold federal income tax as though the employee selected Single or Married Filing Separately and left Steps 2, 3 and 4 blank.
Understanding Exemptions from Withholding
An employee claiming exemption from federal income tax withholding isn’t automatically submitting an invalid Form W-4.
Beginning with the 2026 Form W-4, employees claiming exemption use the exemption checkbox on the form. Generally, an employee may claim exempt status only if they:
- Had no federal income tax liability in 2025, and
- Expect no federal income tax liability in 2026
Determining eligibility is the employee’s responsibility—not the employer’s.
How IRS Lock-In Letters Affect Employers
Employers generally don’t submit Forms W-4 to the IRS unless specifically instructed.
However, if the IRS determines an employee isn’t withholding enough federal income tax, it may issue a lock-in letter directing the employer to withhold taxes using a specified filing status and withholding amount.
Before the lock-in becomes effective:
- The employee receives separate notice from the IRS.
- The employee has an opportunity to dispute the determination directly with the IRS.
Employer Responsibilities After Receiving a Lock-In Letter
Once the lock-in letter takes effect, employers must:
- Follow the IRS withholding instructions.
- Disregard any Form W-4 that would reduce withholding below the required amount.
- Accept a new Form W-4 only if it results in more withholding.
- Configure electronic payroll systems to prevent employees from reducing withholding below the IRS-required amount.
Employers should not reduce withholding unless the IRS authorizes the change. Failure to comply with lock-in instructions may leave the employer responsible for taxes that should have been withheld.
Establish Payroll Procedures for Form W-4 Compliance
Strong payroll procedures help reduce compliance risks.
Your payroll process should include procedures for:
- Receiving Forms W-4
- Reviewing forms for validity
- Retaining employee withholding records
- Responding appropriately to IRS notices
Payroll staff should know how to identify altered or unauthorized forms but should not evaluate whether an employee calculated withholding correctly. That responsibility generally belongs to the employee—and, when necessary, the IRS.
Direct Employees to Reliable Resources
When employees have questions about completing Form W-4, employers should avoid giving individualized tax advice unless qualified to do so.
Instead, refer employees to:
- The IRS Tax Withholding Estimator
- Their personal tax advisor
These resources can help employees determine the correct amount of federal income tax withholding.
Reduce Payroll Compliance Risks
Handling invalid Forms W-4 and IRS lock-in letters correctly helps protect your business from unnecessary payroll tax liabilities and IRS compliance issues.
Whether you’re updating payroll procedures, responding to an invalid Form W-4 or complying with an IRS lock-in letter, having knowledgeable guidance can make the process easier.
THF’s experienced tax professionals can help your business navigate payroll tax compliance and withholding requirements with confidence. Contact us today to learn how we can help.
