Many of the major airlines have announced revised flight-cancellation policies as a result of the implementation of codes red and orange on some international and domestic travel.
American Airlines has the most generous policy, allowing for changes or refunds on both domestic and international travel within certain date ranges, with no penalty.
Other affected airlines with policy changes or advisories are:
USA Today has put together a detailed acount of airline cancellation policies as well.
More carriers may announce new policies in the hours and days ahead. Be sure to check with your airline if you need or want to change your flight due to the new security measures.