NEW YORK (AP) — Air travelers across the United States are bracing for worsening delays and cancellations this week unless lawmakers can come to an agreement to end the ongoing federal government shutdown.

On Saturday, U.S. airlines were forced to cut over 1,500 flights, and more than 2,900 were scrapped on Sunday after the Federal Aviation Administration instructed carriers to reduce traffic due to staffing shortages. The shortage is mainly a result of unpaid air traffic controllers calling out. Many of these workers have now missed nearly a full month’s pay.

By early Monday, nearly 1,600 Monday flights had already been canceled, with close to 1,000 more scheduled for cancellation on Tuesday.

The Senate made some progress toward resolving the impasse on Sunday, but a final agreement may still be days away. Even when a deal is reached, airline operations may take time to return to full capacity.

Travelers are seeing increasing delays at major hubs. Airports in Newark, Orlando, Chicago, and Detroit are experiencing wait times of more than an hour, with delays expected to grow, according to data from FlightAware.

This marks the second consecutive missed paycheck for air traffic controllers. Union leader Nick Daniels is scheduled to speak at a news conference Monday morning to discuss the challenges the shutdown has created for air traffic personnel.

Experts warn that the situation for airlines could deteriorate further as flight crews and equipment are increasingly tied down due to reduced support from air traffic control teams.

The FAA required a 4% cut in nationwide flight operations over the weekend, a figure expected to increase to 6% on Tuesday and 10% by the weekend. Transportation Secretary Sean Duffy mentioned during a Sunday television appearance that the reduction could climb to 20% if the shutdown persists.

"Every day without pay, fewer controllers are showing up," said Duffy, noting how the financial strain is driving workers away.

The FAA has been dealing with a long-standing controller shortage, and several administrations have tried without success to encourage experienced staff to delay retirement. Duffy noted the shutdown is making that issue worse, with some controllers opting to leave the workforce earlier than planned.

Though a 4% cut in flights may seem minor, the effects are heavily concentrated at the busiest 40 airports in the country, leading to outsized disruption. FAA officials argue the reductions are vital to ensure safety, as remaining staff are working extended hours and are under significant stress due to mandatory overtime and lack of pay.

The outlook remains grim, particularly with the holiday season approaching. If conditions don’t improve, Duffy warned air traffic may slow to a crawl by Thanksgiving week.

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Associated Press writers Stephen Groves and Kevin Freking contributed to this report from Washington. Rio Yamat also contributed from Las Vegas.