20 C.F.R. § 203.1
The term "employee" means (1) any individual in the service of one or more employers for compensation, (2) any individual who is in the employment relation to one or more employers, and (3) an employee representative. The term "employee" shall include an employee of a local lodge or division defined as an employer in sub-section (a) only if he was in the service of or in the employment relation to a carrier on or after the enactment date. The term "employee representative" means any officer or official representative of a railway labor organization other than a labor organization included in the term "employer" as defined in section 1(a) who before or after the enactment date was in the service of an employer as defined in section 1(a) and who is duly authorized and designated to represent employees in accordance with the Railway Labor Act, as amended, and any individual who is regularly assigned to or regularly employed by such officer or official representative in connection with the duties of his office.
The term "employee" shall not include any individual while such individual is engaged in the physical operations consisting of the mining of coal, the preparation of coal, the handling (other than movement by rail with standard railroad locomotives) of coal not beyond the mine tipple, or the loading of coal at the tipple.
An individual is in the service of an employer whether his service is rendered within or without the United States if (i) he is subject to the continuing authority of the employer to supervise and direct the manner of rendition of his service, or he is rendering professional or technical services and is integrated into the staff of the employer, or he is rendering, on the property used in the employer's operations, other personal services the rendition of which is integrated into the employer's operations, and (ii) he renders such service for compensation, or a method of computing the monthly compensation for such service is provided in section 3(c): Provided, however, That an individual shall be deemed to be in the service of an employer, other than a local lodge or division or a general committee of a railway-labor-organization employer, not conducting the principal part of its business in the United States only when he is rendering service to it in the United States; and an individual shall be deemed to be in the service of such a local lodge or division only if (1) all, or substantially all, the individuals constituting its membership are employees of an employer conducting the principal part of its business in the United States; or (2) the headquarters of such local lodge or division is located in the United States; and an individual shall be deemed to be in the service of such a general committee only if (1) he is representing a local lodge or division described in clauses (1) or (2) immediately above; or (2) all, or substantially all, the individuals represented by it are employees of an employer conducting the principal part of its business in the United States; or (3) he acts in the capacity of a general chairman or an assistant general chairman of a general committee which represents individuals rendering service in the United States to an employer, but in such case if his office or headquarters is not located in the United States and the individuals represented by such general committee are employees of an employer not conducting the principal part of its business in the United States, only such proportion of the remuneration for such service shall be regarded as compensation as the proportion which the mileage in the United States under the jurisdiction of such general committee bears to the total mileage under its jurisdiction, unless such mileage formula is inapplicable in which case the Board may prescribe such other formula as it finds to be equitable, and if the application of such mileage formula, or such other formula as the Board may prescribe, would result in the compensation of the individual being less than 10 per centum of his remuneration for such service no part of such remuneration shall be regarded as compensation: Provided further, That an individual not a citizen or resident of the United States shall not be deemed to be in the service of an employer when rendering service outside the United States to an employer who is required under the laws applicable in the place where the service is rendered to employ therein, in whole or in part, citizens or residents thereof; and the laws applicable on August 29, 1935, in the place where the service is rendered shall be deemed to have been applicable there at all times prior to that date.
20 C.F.R. § 203.1