The Federal Aviation Administration will reduce flight capacity by 10% at 40 major airports across the country, officials announced during a press conference on Wednesday.

The decision could cut thousands of flights per day.

The restrictions will go into effect Friday morning, FAA Administrator Bryan Bedford and Transportation Secretary Sean Duffy said. The airports that will be impacted will be announced on Thursday, officials said.

“Our sole role is to make sure that we keep this airspace as safe as possible. Reduction in capacity at 40 of our locations. This is not based on light airline travel locations. This is about where the pressure is and how to really deviate the pressure,” said Bedford. 

This comes after Duffy said earlier this week that the FAA will be forced to shut down the airspace in some areas if the shutdown continues into next week.

The forthcoming reduction in capacity marks an unprecedented move by the FAA and the Department of Transportation. Bedford said he has never seen this happen before in his 35-year career.

Airlines for America, a trade association representing many major U.S. airlines, released a statement after the announcement, saying, “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.”

This is a developing story. Please check back for updates.