"In addition to expatriation proposals, some Members of Congress have advocated and/or sponsored bills to deny or revoke passports for U.S. citizens fighting or planning to fight abroad for foreign terrorist groups such as the Islamic State in Iraq and Syria (ISIS). These Members are concerned about the possibility that such citizens may return to the United States to perpetrate terrorist acts on U.S. soil or may flout U.S. foreign policy by continuing to fight abroad for such groups. The latter is particularly a concern since President Obama's announcement of a plan for U.S. involvement in combating ISIS abroad, the enactment of congressional authorization for aid to Syrian rebels opposed to ISIS, and potential congressional debate and authorization for further U.S. military action against ISIS. Denial or revocation of a passport for a person in the U.S. would prevent a U.S. citizen from leaving the country lawfully because statute and regulations generally require a U.S. citizen to present a U.S. passport when departing or entering the U.S. Advocates of revoking a passport for a U.S. citizen outside the U.S. believe that this would not only prevent U.S. 'foreign fighters' from traveling freely outside the U.S., but would also prevent their reentry into the U.S. to engage in terrorism in U.S. territory. Federal courts have, however, recognized a citizen's right to enter the U.S., even without a passport."
CRS Legal Sidebar, October 10, 2014