27 CFR §17.23

1. (a)Use Form SS-4. A claimant must obtain an employer identification number (EIN) by filing an application with the Internal Revenue Service (IRS) on IRS Form SS-4. Form SS-4 is available from the local IRS Service Center, from the IRS District Director, the IRS Web site at https://www.irs.gov or from the TTB National Revenue Center. The claimant must file this form with IRS in accordance with the instructions on the form.
2. (b)One EIN only. Each claimant must obtain and use only one EIN, regardless of the number of places of business for which a claim is filed under this part.