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.

For years, the shortage of certified air traffic controllers in the US has led to flight disruptions and headaches for travelers across the country, most recently at busy Newark Liberty International Airport in New Jersey,

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