Transportation Secretary Sean Duffy warned there will be a 10% reduction in air travel capacity at 40 major airports in the US starting Friday morning, if the government shutdown continues.

The decision was made because air traffic controllers have been reporting issues with fatigue, the head of the Federal Aviation Administration (FAA) said at a briefing with Duffy on Wednesday.

It is unusual, just as the shutdown is unusual, just as the fact that our controllers haven't been paid for a month is unusual, said FAA chief Bryan Bedford.

During the shutdown, now the longest in US history, controllers have had to keep working without pay, prompting some to call out sick or take side jobs.

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, Reuters reported after the announcement, citing four unnamed sources.

The names of the affected airports - all high-traffic locations - will be released on Thursday, the officials said.

The cancellations could affect between 3,500 and 4,000 flights per day.

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.

Duffy said air travel is still safe, and the decision to cancel the flights was being made to maintain safety and efficiency.

If the shutdown continues and adds more pressure to the system, additional restrictive measures may be required, Bedford said.

A spokesperson for Southwest Airlines stated that the company is still evaluating how the flight restrictions will affect its services, while urging Congress to resolve its impasse.

Nick Daniels, the president of the labor union representing over 20,000 aviation workers, described the dire situation, stating controllers are struggling to afford gas to commute to work amidst their unpaid status.

The ongoing shutdown, which began on October 1, has left many essential federal staff, including air traffic controllers, working without compensation.

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