Pursuant to IRS Publication 15, an employee claiming exemption from federal withholding can do so only by filing Form W-4 with their employer. This filing is only effective for the calendar year for which it is filed. To continue exempt filing status, each impacted employee must file a new Form W-4 by February 15 of the new calendar year. If the employer (agency) does not receive a new W-4 by February 15, 2017 they must begin withholding based on the last W-4 for the employee that did not claim exemption. If one is not available (not filed), then taxes should be withheld on the basis of 'single with zero withholding allowances'. If an employee provides a new Form W-4 after February 15, 2017 it will apply to future wages only. No refund of taxes previously withheld will be made.