A Federal Employer Identification Number or FEI is a number issued by the Internal Revenue Service (IRS). The FEI number is also called the EIN number. This number is used to identify the business entity for federal tax purposes. You must submit an SS-4 form to the Internal Revenue Service to obtain a Federal Employer Identification Number or determine if your business entity is required to have one. You may reach the IRS by calling 1-800-829-4933 or visiting their web site www.irs.gov.