United Airlines suggested Wednesday that an air traffic controller shortage is to blame for “significant delays” at its Newark Liberty International Airport (EWR) hub, as people in the U.S. began their holiday travel.

The lawmakers stressed that while progress has been made in addressing aging ATC systems, gaps in oversight remain. They criticized the FAA’s acquisition oversight council for inconsistencies in assessing high-risk factors, which they argue hinder the timely and cost-effective delivery of modernization projects.