According to the IRS, if you are a
sole proprietor who has
no employees and who files no excise or pension tax returns, you
can use your social security number as your identification
Otherwise, you must have an employer identification number (EIN)
if your business fits any of these situations:
You are a corporation
You pay wages to one or more employees.
You file pension and excise tax returns.
You get a Federal EIN from the IRS by applying online, by phone, by FAX, by mail, or at a local IRS office.
For detailed instructions on applying for an EIN, visit the How to apply for a federal EIN page on payroll.com.