20 C.F.R. § 404.1004

(a) General requirements of employment. Unless otherwise excluded from coverage under §§ 404.1012 through 404.1038, the work you perform as an employee for your employer is covered as employment under social security if one of the following situations applies:

(1) You perform the work within the United States (whether or not you or your employer are a citizen or resident of the United States).

(2) You perform the work outside the United States and you are a citizen or resident of the United States working for—

(i) An American employer; or

(ii) A foreign affiliate of an American employer that has in effect an agreement covering your work under section 3121(l) of the Code.

(3) You perform the work on or in connection with an American vessel or American aircraft and the conditions in paragraphs (a)(3) (i) and (ii) are met. Your citizenship or residence does not matter. The citizenship or residence of your employer matters only if it affects whether the vessel is an American vessel.

(i) You enter into the contract of employment within the United States or the vessel or aircraft touches at a port or airport within the United States during the performance of your contract of employment on the vessel or aircraft.

(ii) You are employed on and in connection with the vessel or aircraft when outside the United States.

(4) Your work is designated as employment or recognized as equivalent to employment under a totalization agreement. (See § 404.1913. An agreement may exempt work from coverage as well as extend coverage to work.)

(5) Your work performed after December 31, 1994, is in the employ of an international organization pursuant to a transfer from a Federal agency under section 3582 of title 5 of the United States Code and both the following are met:

(i) Immediately before the transfer, your work for the Federal agency was covered employment; and

(ii) You would be entitled, upon separation from the international organization and proper application, to reemployment with the Federal agency under section 3582.

(b) Explanation of terms used in this section—(1) American employer means—

(i) The United States or any of its instrumentalities;

(ii) A State, a political subdivision of a State, or an instrumentality of any one or more States or political subdivisions of a State;

(iii) An individual who is a resident of the United States;

(iv) A partnership, if at least two-thirds of the partners are residents of the United States;

(v) A trust, if all of the trustees are residents of the United States; or

(vi) A corporation organized under the laws of the United States or of any State.

(2) American aircraft means an aircraft registered under the laws of the United States.

(3) American vessel means a vessel documented or numbered under the laws of the United States. It also includes a vessel neither documented nor numbered under the laws of the United States, nor documented under the laws of any foreign country, if its crew is employed solely by one or more citizens or residents of the United States, or corporations organized under the laws of the United States or of any State.

(4) Citizen of the United States includes a citizen of the Commonwealth of Puerto Rico, the Virgin Islands, Guam, American Samoa or the Commonwealth of the Northern Mariana Islands.

(5) Foreign affiliate refers to a foreign affiliate as defined in section 3121(l)(6) of the Code.

(6) On and in connection with refers to the performance of work on a vessel or aircraft which concerns the vessel or aircraft. Examples of this kind of work are the services performed on a vessel by employees as officers or crew members, or as employees of concessionaires, of the vessel.

(7) On or in connection with refers to work performed on the vessel or aircraft and to work which concerns the vessel or aircraft but not actually performed on it. For example, shore services in connection with repairing, loading, unloading, or provisioning a vessel performed by employees as officers or crew members, or as employees of concessionaires, of the vessel are included, since this work concerns the vessel though not performed on it.

(8) State refers to the 50 States, the District of Columbia, the Commonwealth of Puerto Rico, the Virgin Islands, Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands.

(9) United States when used in a geographical sense means the 50 States, the District of Columbia, the Commonwealth of Puerto Rico, the Virgin Islands, Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands.