The Federal Aviation Administration (FAA) plans to reduce air traffic by 10% at dozens of busy airports during the closure

WASHINGTON (AP) — The Federal Aviation Administration said Wednesday it will reduce air traffic by 10% across 40 “high volume” markets starting Friday morning to maintain safety during the ongoing government shutdown.

The reduction is expected to affect thousands of flights across the country because the FAA directs more than 44,000 flights daily, including commercial passenger flights, cargo planes and private jets.

Air traffic controllers have been working without pay since the lockdown began on October 1. As some were called back to their jobs, staff shortages during some shifts led to flight delays at a number of US airports.

Read more: What to do if your flight is delayed or canceled during a government shutdown

Citing mounting staffing pressures, FAA Administrator Brian Bedford said the agency will not wait for a crisis to act.

“We cannot ignore that,” he added.

Bedford and Transport Minister Sean Duffy said they would meet with airline executives later Wednesday to determine how to safely implement the flight reductions. Even then, both declined to name the affected markets. Bedford said the list will be released sometime Thursday.

“If pressures continue to mount even after we take these measures, we will come back and take additional measures,” Bedford said.

The Associated Press on Wednesday sent requests for comment on the FAA’s decision to major U.S. airlines, including Delta, United and American Airlines.

Southwest Airlines said it is evaluating potential impacts to its schedule and will reach out as soon as possible to customers whose travel plans may be affected.

“We continue to urge Congress to immediately resolve the impasse and return the national airspace system to full capacity,” the company said.

The FAA sometimes slows or stops flights from taking off toward the airport due to weather conditions or when there are not enough controllers and other personnel or facilities are unable to pick up the slack. Last weekend saw some of the worst staff shortages of the lockdown, which became the longest on record early Wednesday.

From Friday through Sunday evening, at least 39 different air traffic control facilities declared some capacity for a limited number of staff, according to an Associated Press analysis of operations plans sent through the air traffic control system’s command center system. This number, which is likely to be an undercount, is well above the average on the weekends before the lockdown

During the weekend periods from Jan. 1 to Sept. 30, an average number of airport towers, regional hubs that oversee many airports and facilities that monitor traffic at higher altitudes, reported a probability of staffing issues of 8.3, according to an AP analysis. But over the five weekend periods since the shutdown began on Oct. 1, the average has more than tripled to 26.2 establishments.

He watches: The closure puts further pressure on the air traffic control system, which is already understaffed

Most probationers continued to work mandatory overtime six days a week during the shutdown. This leaves little time for a side job to help cover bills, mortgage payments and other expenses unless supervisors call in.

Major airlines, airline unions and the broader travel industry have urged Congress to end the shutdown.

Wednesday’s announcement followed Duffy’s warning the previous day of the potential for chaos in the skies next week if the shutdown lasts long enough for air traffic controllers to lose their second full pay next Tuesday.

The FAA wanted to take a proactive approach rather than react after a disaster strikes, Duffy said. He pointed to the fatal mid-air collision in January between a commercial plane and a military helicopter near Ronald Reagan Washington National Airport.

“We’ve learned from that,” Duffy said. “Now we look at the data, and before it becomes a problem, we try to assess the pressures and we try to take steps before there are negative consequences.” “And that’s what’s happening here today.”

Associated Press journalist Christopher L. Keller contributed from Albuquerque, New Mexico.