Each agency may require employees or members of the Armed Forces under its jurisdiction to complete a withholding certificate in order to calculate the amount to be withheld. The agency shall use the withholding certificate which the State, city or county has prescribed. Where the State, city or county has not prescribed a certificate, the agency may use a certificate approved by the Department of the Treasury. The agency may rely on the information in the certificate. Copies of completed certificates shall be provided to the taxing authority by agencies upon request.
31 C.F.R. §215.8