ABC News has learned the U.S. government is concerned about attacks using overseas airliners, because some of the air crews may be Al Qaeda sympathizers, trained long ago for missions.
U.S. security officials have issued new directives to international airports and airlines. If they aren't followed, they won't be let into the country; of particular concern, France and Mexico.
The Wall Street Journal reports homeland security is also looking into flights from Canada and Latin American countries.
The Pentagon says Americans should not be surprised to see more military aircraft in the skies.
"They may see additional air patrols over select cities and facilities, an increase in the air defense posture here in Washington, D.C., and combat aircraft could be put on a higher alert at different air bases throughout the country," said Richard Myers, Chairman of the Joint Chiefs of Staff.
Travelers are certainly aware of the heightened state of alert on the nation's roads and at airports, but for many, just getting everything done before the holidays is the higher priority.
"We're free people. We shouldn't sit around, you know, hiding under chairs and hoping it will go away. We have to live our lives and that's what we'll all do," said Donald Rumsfeld, Secretary of Defense.
Part of the reason why the alert was called is because it is the holiday season, but depending on further intelligence that's gathered, the orange alert may be in effect through the new year.