Employer Identification Numbers, also known as Federal Tax Identification Numbers, are assigned by the Internal Revenue Service. An EIN is a nine-digit number used to identify tax accounts of employers and specific other entities that have no employees, according to the IRS.
EINs are used by most businesses such as sole proprietors, employers, corporations, partnerships and non-profit associations. One can apply for an EIN online, by fax or by mail, and there is a limit of one EIN issued per responsible party per day, notes the IRS. When applied for online, an EIN is issued immediately. EINs applied for by fax are issued within four business days and those applied for by mail are issued within four to five weeks. The online system is available Monday through Friday from 5 a.m. to 10 p.m. EST at the IRS website.