Which document specifies the number of exemptions an employee should claim for withholding purposes?

The document that specifies the number of exemptions an employee should claim for withholding purposes is the W-4 Form. This form is used by employees to indicate their tax situation to their employer, including how many withholding allowances they claim, which in turn affects the amount of federal income tax withheld from their paychecks. Employees can adjust their withholdings based on their personal financial situations, such as dependents, filing status, and other considerations.

The W-2 Form is a summary of an employee’s annual earnings and the taxes withheld from their pay but does not allow for exemptions to be claimed. The Lock-in Letter is issued by the IRS to employers when an employee's claimed exemptions appear to be inappropriate, but it does not serve as the means for the employee to declare exemptions themselves. The ITIN Application is related to obtaining an Individual Taxpayer Identification Number for individuals who do not have a Social Security number, and does not pertain to withholding exemptions for payroll purposes.