27 CFR §19.243

1. (a)Use Form SS-4. The proprietor must obtain an employer identification number (EIN) by filing an application with the Internal Revenue Service (IRS) on Form SS-4. Form SS-4 is available from Internal Revenue Service Centers, from IRS District Directors, the IRS Web site at https://www.irs.gov, or from TTB's National Revenue Center. The proprietor may file this form with IRS by mail, telephone, or fax by following the instructions on the form.
2. (b)Time limit. If the proprietor has not already received, or applied for, an EIN at the time that the first return on form TTB F 5000.24, Excise Tax Return, is filed, the proprietor must file such application for an EIN not later than seven days from the date of filing the TTB F 5000.24.
3. (c)One EIN only. Each proprietor must obtain and use only one EIN, regardless of the number of places of business for which the proprietor is required to file a tax return under this subpart.