Federal officials announced that the U.S. will reduce air traffic by 10% across 40 “high-volume” markets starting on Friday, citing staffing shortages related to the ongoing government shutdown.

“We have decided that a 10% reduction in scheduled capacity would be appropriate to continue to take the pressure off of our controllers,” Federal Aviation Administration Administrator Bryan Bedford said at a press conference on Wednesday. 

Bedford and U.S. Transportation Secretary Sean Duffy said the new measures are necessary to keep air travel safe, as pressures on air traffic controllers mount during the longest government shutdown in history. 

Bedford said he would specify which 40 markets around the country will be affected on Thursday, adding that the restrictions will affect commercial airspace and other activities, including space launches.

More air traffic controllers are exhibiting fatigue as they work without pay during the congressional stalemate, now in its 36th day, Bedford added. Thursday will mark one month since controllers were last paid. 

Airlines, aviation unions and the wider travel industry have urged Congress to end the shutdown.

More than 10,000 flights within, into or out of the U.S. experienced delays last weekend, while roughly 11,000 trips have been delayed this week, according to tracking service FlightAware. 

Bedford and Duffy said they will consult later Wednesday with airline industry executives to discuss how to safely implement the reduction in flights.

“The early indicators are telling us we can take action today to prevent things from deteriorating,” Bedford said.

The U.S. struggled to recruit sufficient numbers of air traffic controllers even before the shutdown began, with Duffy saying that the country needs an additional 2,000 controllers.