(AP) — Shortages of air traffic controllers are straining operations — with flight disruptions piling up nationwide — as the shutdown drags on. Newark Airport in New Jersey experienced delays of two to three hours on Sunday, and busy hubs like George Bush Intercontinental Airport in Houston, Dallas Fort Worth International Airport and Chicago O’Hare saw dozens of weekend disruptions.

Experts, as well as union leaders representing air traffic controllers and security screeners, warn of significantly worse impacts the longer workers go without a paycheck. The Federal Aviation Administration said Friday that nearly 13,000 air traffic controllers had been working without pay for weeks.