With the new tax reform, comes new tax tables for employees. Employers should begin using the new tax withholdings as soon as possible, but no later than February 15, 2018. Although you are not required to have employees fill out a new W-4, you should consider letting the employee know that their taxes might change and therefore their paycheck may be affected. If they would like to change their withholding information, have them fill out a new W-4. The 2018 W-4 has not been released by the Internal Revenue Service (IRS).