(a) An individual shall not be an employee by reason of rendition of service to 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 except while engaged in performing service for it in the United States.

(b) An individual shall not be an employee by reason of rendition of service to a local lodge or division, unless:

(1) All, or substantially all the individuals constituting the membership of such local lodge or division 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.

(c) An individual shall not be an employee by reason of rendition of service to a general committee of a railway-labor-organization employer, unless:

(1) Such individual is representing a local lodge or division, all or substantially all of whose members are employees of an employer conducting the principal part of its business in the United States, or the headquarters of such local lodge or division is located in the United States; or

(2) All or substantially all the individuals represented by such a general committee are employees of an employer conducting the principal part of its business in the United States; or

(3) Such an individual 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; Provided, however, That if the office or headquarters of such general chairman or assistant general chairman is not located within the United States he will not be an employee unless 10 percent or more of his remuneration for service as general chairman or assistant general chairman is creditable as compensation, the creditable compensation to be computed according to the proportion which the mileage in the United States under the jurisdiction of such general committee bears to the total mileage under its jurisdiction, or according to a formula to be prescribed by the Board if the mileage formula is inapplicable.