If you are a sole proprietor who has employees, or you are a partnership or incorporated, you will have to get a federal tax ID number, also known as an Employer Identification Number (EIN). If you are a sole proprietor with no employees, your social security number will serve as your ID number.
You use your EIN for filing and paying the various withholding and social security taxes you are required to make as an employer.
To get an EIN, you fill out and file Form SS-4 with the Internal Revenue Service. You can get this form from your local IRS office, or by calling the IRS help line at 800-829-3676 (800-TAX-FORM).
You may also be required to get a separate state tax ID number. Check with the state agency responsible for collecting taxes (often your state department of taxation or state treasury department) for the correct forms. You can find the address and phone number in the government blue pages of your local phone directory.