Have a Tax Question? Ask a Tax Expert
You are correct. For your employee to request a withholding change he is required to supply you with a W4.
He can request an additional dollar amount to be added to the withholding but not a flat rate.
If he does not complete any W4 then the withholding defaults to Single and Zero.
Tell him it is to his benefit to complete the W4.
If my answer addressed your question please rate below or above (let me know if you have difficulty as I believe the system changed), if you need more information reply below.