As an individual filing federal taxes, you will need your Social Security number (SSN) to identify yourself with the Internal Revenue Service (IRS). You will also need your employer’s federal employer identification number (EIN) to report your wages and tie your earnings to the company from which you earned them. Your employer’s EIN is similar to your SSN in that it identifies the company with the IRS. Just as your employer needs your SSN for its records and tax filing, you are entitled to its EIN, and the information is readily available to you in several ways.
TL;DR (Too Long; Didn't Read)
Your employer’s federal employer identification number is similar to your own SSN in that it identifies the company with the IRS.
Look on one of your pay stubs from the employer in the current tax year. The EIN is a nine-digit number in the format 12-3456789. For security reasons, your employer is not legally required to list its EIN on pay stubs, but it is common practice and the most convenient place to look.
Call your employer's human resources department and ask for its EIN. Depending on the size of the company, you may have to identify yourself using your SSN before it releases the EIN to you.
Look on your W-2 under your employer's contact information in box "b." The EIN will be listed in the format 12-3456789.