Federal cuts to air-traffic controllers due to the sequester are causing problems at some airports. New York City and Los Angeles have already experienced delays, and other major airports may as well. About 10% of controllers will be furloughed on a given day according to the workers' union. Airlines say that the lack of information on when and where workers will be furloughed is making it difficult to know how it will affect service.
See "NYC Fliers Confront Delays on FAA Controller Furloughs", Mary Jane Credeur and Mary Schlangenstein, Business Week, April 21, 2013