US Transportation Secretary Sean Duffy has warned that air travel capacity will be cut by up to 10% at 40 major airports over the coming days, if the government shutdown continues.
The decision, which is expected to affect domestic flights only, was made because air traffic controllers had been reporting fatigue, the head of the Federal Aviation Administration (FAA) said at a briefing alongside Duffy.
Some 1.4 million federal workers, from air traffic controllers to park wardens, are working without pay - or are on forced leave - because the US Congress has not agreed a federal funding budget.
Unions say many employees are becoming ill with stress or are being forced into taking second jobs.
On Wednesday, the impasse became the longest shutdown in US history.
It is unusual, said FAA chief Bryan Bedford of the planned flight reductions, just as the shutdown is unusual, just as the fact that our controllers haven't been paid for a month is unusual.
The flight reductions will be gradual, starting at 4% of domestic flights on Friday, then rising to 5% on Saturday and 6% on Sunday, before hitting the full 10% next week, the Reuters news agency reported, citing four unnamed sources.
The names of the affected airports - all high-traffic locations - would be released on Thursday, the officials said.
US media including the BBC's partner CBS News reported that the list would include some of the nation's busiest hubs, including Hartsfield-Jackson Atlanta International, Dallas/Fort Worth International, Denver International, Chicago O'Hare International, and Los Angeles International.
The cancellations could affect between 3,500 and 4,000 flights per day. US media also reported that international flights would not be affected.
We are seeing pressures build in a way that we don't feel - if we allow it to go unchecked - will allow us to continue to tell the public that we operate the safest airline system in the world, Bedford said during Wednesday's briefing.
Duffy insisted that air travel was still safe, and the decision to cancel the flights was being made to maintain safety and efficiency.
If the shutdown continued and added more pressure to the system, additional restrictive measures may be required, Bedford said.
