The United States can deny application for or completely revoke Americans' passports for a number of reasons: if they get committed to a mental institution, fall behind on child-support payments, or join an enemy nation's army.
Several lawmakers this week have called upon that last reason to justify revoking the passports of Americans who are fighting for the Islamic State in Iraq and Syria. But for the more than 100 Americans believed to be fighting alongside the terrorist group in the Middle East, the U.S. does not specifically have the power to revoke their passports.
That's because ISIS is not a foreign state. According to the Immigration and Nationality Act, the U.S. can revoke the passport of any citizen who fights in the military of a country hostile to America. ISIS, which in the last month publicly beheaded two American journalists, is certainly hostile. But its status as a terrorist group rather than a recognized foreign state leaves the passports of Americans who join their cause untouched.
At a hearing of the House Homeland Security Subcommittee Wednesday, Republican Rep. Jeff Duncan of South Carolina lamented what to him seem like semantics. "This is a real threat," he said. "We need to revoke the passports of Americans that have gone to fight there."