I am trying to find out what US law says about foreign travelers flying between US territories and the "mainland." For example, flying from Guam to Hawaii or from Puerto Rico to Florida.
(g) The term geographical part of the United States means:
(1) The continental United States,
(4) Puerto Rico,
(5) The Virgin Islands,
(7) American Samoa,
(8) Swains Island, or
(9) The Commonwealth of the Northern Mariana Islands (beginning November 28, 2009).
(h) The term depart from the United States means depart by land, water, or air:
(1) From the United States for any foreign place, or
(2) from one geographical part of the United States for a separate geographical part of the United States: Provided, That a trip or journey upon a public ferry, passenger vessel sailing coastwise on a fixed schedule, excursion vessel, or aircraft, having both termini in the continental United States or in any one of the other geographical parts of the United States and not touching any territory or waters under the jurisdiction or control of a foreign power, shall not be deemed a departure from the United States.
US Customs and Border Protection's page on the matter is terribly confusing and does not adequately address the case of someone who is neither a US citizen nor lawful permanent resident. However, it does seem to imply that a foreigner requires a passport to fly between territories and states:
Will travelers from U.S. territories need to present a passport to enter the United States?
U.S. Citizens and Lawful Permanent Residents (LPR's) who travel directly between parts of the United States, which includes Guam, Puerto Rico, U.S. Virgin Islands, American Samoa, Swains Island and the Commonwealth of the Northern Mariana Islands (CNMI), without touching at a foreign port or place, are not required to present a valid U.S. Passport or U.S. Green Card.
However, it is recommended that travelers bring a government issued photo ID and copy of birth certificate.
It also is recommended that you carry proof of your LPR status at all times in the event you are asked to prove your status. This may be in the form of a green card or passport.
Hawaii is a U.S. state and therefore passport documentation requirements for U.S. citizens and LPR's do not apply.
Entry requirements for non-U.S. citizens are the same as for entering the United States from any foreign destination. Upon departure, a passport is required for all but U.S. citizens.
Questions about requirements for domestic travel should be directed to Transportation Security Administration (TSA). TSA can be reached at 1-866-289-9673.
This seems to imply that the rules are different for travel between (for example) Alaska and Hawaii than they are between Guam and Hawaii, even though there is no such distinction to be found in the regulation.
Furthermore, at 8 USC 1101(a)(38), the general definition of "United States" for the purpose of immigration law is given as
(38) The term “United States”, except as otherwise specifically herein provided, when used in a geographical sense, means the continental United States, Alaska, Hawaii, Puerto Rico, Guam, the Virgin Islands of the United States, and the Commonwealth of the Northern Mariana Islands.
It is therefore odd that the text makes a distinction between such travel and "domestic travel," when it seems that according to immigration law such travel is domestic travel.
Is there some other basis to be found in US law for a requirement that foreigners have a passport when flying directly between US territories or between a US territory and a US state? Is there some basis that justifies treating these flights differently from flights to or from Alaska or Hawaii?