US airlines canceled 1,330 flights on the second day of government-mandated flight cuts across the country on Saturday, and the industry braced for more cancellations as the federal government shutdown continued.

The Federal Aviation Administration had instructed airlines to reduce daily flights by four percent starting Friday at 40 major airports due to concerns about air traffic control safety.

The shutdown has led to a shortage of air traffic controllers because they have not received their salaries for weeks.

The discounts on flights will increase to six percent on Tuesday before reaching ten percent by November 14.

The Federal Aviation Administration reported on Saturday problems with air traffic controllers at 25 airports and other hubs, causing flight delays in at least 12 major U.S. cities, including Atlanta, Newark, San Francisco, Chicago, and New York.

Around 5,450 flights were delayed on Saturday, following the delay of 7,000 flights and the cancellation of 1,025 flights on Friday.

During the extended government shutdown, now in its 39th day, 13,000 air traffic controllers and 50,000 security personnel have been forced to work without pay, leading to increased absenteeism. Several air traffic controllers were notified on Thursday that they will not receive any compensation for the second consecutive pay period next week.

U.S. Transportation Secretary Sean Duffy said he might request a 20 percent reduction in air traffic if more controllers stopped coming to work, adding, I'm evaluating the data. We'll make decisions based on what we see in the airspace.

The Trump administration cited air traffic control problems as Republicans tried to pressure Senate Democrats into supporting what they called a clean, unfettered government funding bill. Democrats blame the shutdown on Republicans' refusal to negotiate on subsidies for health insurance that are set to expire at the end of this year.