Form W-4 Employee's Withholding Allowance Certificate
Each W-4 should include each employee's name and Social Security Number (SSN). (This requirement also applies to resident and nonresident alien employees.) You should ask your employee to show you his or her social security card.
A W-4 is used to know how much income tax to withhold from employees' wages. The amount of income tax withholding must be based on filing status and withholding allowances claimed on the W4 form. If a new employee does not give you a completed Form W-4, withhold tax as if he or she is single, with no withholding allowances. If an employee is exempt from income tax withholding, they must indicate this on their W-4.
W-4 remains in effect until the employee gives you a new one. If employees claim exemption from income tax withholding, they must give you a new Form W-4 each year. For more information refer to IRS Publication 15 Circular E, Employer's Tax Guide.
Some states will also have additional withholding forms to complete. Check with your state for additional forms and instructions.