US Internal Revenue Code Section 3402 Income Tax Withholding at Source (26 USC 3402) 3402d-tax-paid-by-recipient: If withholding was missed and the employee later pays the tax, the tax is not collected again from the employer, but penalties and additions remain

What does 3402d-tax-paid-by-recipient require?

Where an employer fails to withhold in breach of the chapter and the income tax against which the withheld amount would have been credited is afterwards paid by the employee, the tax that should have been withheld is not collected from the employer. The subsection does not relieve the employer of penalties or additions to tax for the failure, and the employer must be able to show the employee's payment (the IRS Form 4669 and 4670 process) to claim the relief.