26 CFR § 31.3121(b)(11)-1 - Services in the employ of a foreign government.
(a) Services performed by an employee in the employ of a foreign government are excepted from employment. The exception includes not only services performed by ambassadors, ministers, and other diplomatic officers and employees but also services performed as a consular or other officer or employee of a foreign government, or as a nondiplomatic representative thereof.
(b) For purposes of this exception, the citizenship or residence of the employee is immaterial. It is also immaterial whether the foreign government grants an equivalent exemption with respect to similar services performed in the foreign country by citizens of the United States.