United Airlines said Tuesday an acute shortage of air traffic controllers is causing "significant disruption" for travelers at its busy Newark, New Jersey, hub outside New York. United said the Federal Aviation Administration has been forced to reduce traffic flows to the Newark hub because of low staffing on 12 of the first 25 days of November, disrupting more than 343,000 United travelers by delays, cancellations, long taxi times, and longer flight times related to air traffic control delays for Newark.