26 C.F.R. § 301.7701-12

For purposes of this chapter, the term employer identification number means the taxpayer identifying number of an individual or other person (whether or not an employer) which is assigned pursuant to section 6011 (b) or corresponding provisions of prior law, or pursuant to section 6109, and in which nine digits are separated by a hyphen, as follows: 00-0000000. The terms “employer identification number” and “identification number” (defined in § 31.0-2(a)(11) of this chapter (Employment Tax Regulations)) refer to the same number.