Your employer's tax ID number -- a unique number that identifies it for federal tax reporting-- usually is listed in Box B of Form W-2. If the tax ID number is missing or inaccurate, reach out to the IRS and use a substitute Form W-2 to file your tax return.
Contact the IRS
The IRS specifically outlines the steps a taxpayer should take if he doesn't receive a W-2 or an employer's tax ID number. First, contact your employer about the issue. If it doesn't respond with the information in a reasonable amount of time, and you don't have what you need by February 14, contact the IRS at 1-800-829-1040. During the call, the IRS will ask you for your personal information -- such as your name, address and Social Security number -- and for your employer's name, address and phone number, along with dates of employment and the amount of wages you earned.
Use Form 4852
If you haven't gotten the federal tax ID number by mid April, you still must file your tax return. Use Form 4852, Substitute for Form W-2, to record what information you do have. If you're not sure of your gross income, make your best guess based on your pay stubs. If you're owed a tax refund, expect a delay. It may take the IRS additional time to process your refund while they attempt to verify your employment information.
Amend Your Tax Return if Necessary
If you discover your employer's federal tax ID number after you file the return, update your tax information. Complete Form 1040X to amend your tax return and include the federal tax ID number. There's no fee or penalty for amending your return.