Code of Federal Regulations Title 45. Public Welfare § 45.162.610 Implementation specifications for covered entities

(a) The standard unique employer identifier of an employer of a particular employee is the EIN that appears on that employee's IRS Form W–2, Wage and Tax Statement, from the employer.

(b) A covered entity must use the standard unique employer identifier (EIN) of the appropriate employer in standard transactions that require an employer identifier to identify a person or entity as an employer, including where situationally required.

(c) Required and permitted uses for the Employer Identifier.