The U.S. Federal Aviation Administration (FAA) will reduce airline traffic by 10 percent at 40 locations beginning on Friday, after the ongoing federal government shutdown became the longest in U.S. history, Transportation Secretary Sean Duffy said on Wednesday.

"We're trying to lean into the fact that when we see pressures building in these 40 markets, we just can't ignore it, and we're not going to wait for a safety problem to truly manifest itself when the early indicators are telling us, we can take action today to prevent things from deteriorating," Duffy said.

"I think it's going to lead to more cancellations that we're going to work with the airlines to do this in a systematic way," he said at a joint press conference with FAA Administrator Bryan Bedford.

Bedford said that a 10-percent reduction in scheduled capacity would be appropriate to "continue to take the pressure off of our (air traffic) controllers, and as we continue to see staffing triggers, there will be additional measures that will be taken in those specific markets."

"I'm not aware in my 35-year history in the aviation market, where we've had a situation where we're taking these kind of measures, and again, we're in a renewed territory in terms of government shutdowns," said Bedford.

Since the U.S. federal government shutdown began, about 13,000 air traffic controllers and roughly 50,000 airport security officers have been forced to work without pay.

An increasing number of employees have taken leave, leading to acute staffing shortages in the aviation industry, worsening flight delays across many regions, and raising concerns over aviation safety.

Data from the U.S. flight-tracking website FlightAware shows that thousands of flights nationwide are experiencing delays each day. More than 4,000 flights within, into, or out of the United States were delayed on Tuesday, following nearly 5,000 delays on Monday.

Airlines for America, a trade group representing major U.S. carriers such as Delta and Southwest, said its members were trying to understand the next steps.

"We are working with the federal government to understand all details of the new reduction mandate and will strive to mitigate impacts to passengers and shippers," it said.

The FAA was scheduled to hold a call with airlines on Wednesday evening to explain how the cuts will be implemented, according to industry sources.

The federal government has mostly closed as Republicans and Democrats are locked in a standoff in Congress over a funding bill. Democrats have insisted they would not approve a plan that does not extend health insurance subsidies while Republicans have rejected that.

The closure, which began October 1, left many low-income Americans without food assistance, closed many government services and led to the furlough of about 750,000 federal employees.

(With input from agencies)