Hundreds of flights were canceled or delayed at Newark Liberty International Airport over the weekend and again on Monday as shortages of air traffic controllers persists, causing flight disruptions at one of the nation’s busiest airports.

On the way: a plan for a new system for the Federal Aviation Administration to manage the roughly 45,000 US flights that carry about 2.9 million passengers each day.

United Airlines announced last week it was cutting 35 roundtrip flights daily from the airport amid air traffic control struggles.