Section 31.3121(b)(4)-1 - Services performed on or in connection with a non-American vessel or aircraft(a) Services performed within the United States by an employee for an employer "on or in connection with" a vessel not an American vessel, or "on or in connection with" an aircraft not an American aircraft, are excepted from employment if- (1) The employee is employed by such employer "on and in connection with" such vessel or aircraft when outside the United States, and(2)(i) The employee is not a citizen of the United States, or(ii) the employer is not an American employer.(b) An employee performs services on and in connection with the vessel or aircraft if he performs services on the vessel or aircraft when outside the United States which are also in connection with the vessel or aircraft. Services performed on the vessel outside the United States by employees as officers or members of the crew, or by employees of concessionaires, of the vessel, for example, are performed under such circumstances, since such services are also connected with the vessel. Similarly, services performed on the aircraft outside the United States by employees as officers or members of the crew of the aircraft are performed on and in connection with such aircraft. Services may be performed on the vessel or aircraft, however, which have no connection with it, as in the case of services performed by an employee while on the vessel or aircraft merely as a passenger in the general sense. For example, the services of a buyer in the employ of a department store while he is a passenger on a vessel are not in connection with the vessel.(c) The expression "on or in connection with" refers not only to services performed on the vessel or aircraft but also to services connected with the vessel or aircraft which are not actually performed on it (for example, shore services performed as officers or members of the crew, or as employees of concessionaires, of the vessel).(d) Services performed within the United States on or in connection with a non-American vessel or aircraft for an employer by an employee who is not a citizen of the United States are excepted from employment, irrespective of whether the employer is or is not an American employer, provided the employee also is employed by such employer on and in connection with the vessel or aircraft when outside the United States. Services performed within the United States on or in connection with a non-American vessel or aircraft by an employee for an employer who is not an American employer also are excepted from employment, irrespective of whether the employee is or is not a citizen of the United States, provided the employee also is employed by such employer on and in connection with the vessel or aircraft when outside the United States. Services performed within the United States on or in connection with a non-American vessel or aircraft for an American employer by an employee who is a citizen of the United States are not excepted from employment under section 3121(b)(4), irrespective of whether the employee is employed by such employer on and in connection with the vessel or aircraft when outside the United States. Further, section 3121(b)(4) does not except from employment services performed within the United States for an employer, whether or not an American employer, on or in connection with a non-American vessel or aircraft by an employee, whether or not a citizen of the United States, who is not also employed by such employer on and in connection with the vessel or aircraft when outside the United States.(e) Services performed outside the United States on or in connection with a vessel not an American vessel, or on or in connection with an aircraft not an American aircraft, by a citizen of the United States as an employee for an American employer are not excepted from employment under section 3121(b)(4), irrespective of whether the employee is employed on and in connection with such vessel or aircraft when outside the United States. Services performed outside the United States on or in connection with a vessel not an American vessel or on or in connection with an aircraft not an American aircraft, either by an employee who is not a citizen of the United States or for an employer who is not an American employer, do not, in any event, constitute employment. See paragraph (c) of § 31.3121(b)-3 , relating to services performed outside the United States which constitute employment.(f) See paragraph (c)(2)(v) of § 31.3121(b)-3 for definitions of "vessel" and "aircraft", § 31.3121(f)-1 , for definitions of "American vessel" and "American aircraft", § 31.3121(e)-1 , for definition of "citizen of the United States", and § 31.3121(h)-1 , for definition of "American employer". 26 C.F.R. §31.3121(b)(4)-1