Transportation Secretary Sean Duffy said Sunday that “15 to 20” air traffic controllers are retiring daily amid the government shutdown.

“I used to have about four controllers retire a day before the shutdown. I’m now up to 15 to 20 a day are retiring,” Duffy told CNN’s Jake Tapper on “State of the Union.” “So, it’s going to be harder for me to come back after the shutdown and have more controllers controlling the airspace.”

“So, this is going to live on in air travel, well beyond the time frame that this government opens back up.”

Air traffic controllers are set to miss their second consecutive paycheck on Tuesday, with many missing work and taking second jobs. Duffy added that 81 controller staffing shortages were reported at facilities across the country on Saturday, an increase of 20 such instances relative to Oct. 31.

As a result of the shortages, the Federal Aviation Administration directed all commercial airlines to cut flights by 4 percent on Friday. In a press conference announcing the move on Thursday, Duffy called the measure “proactive” and an attempt to keep the country’s airspace safe.

Updated 4:17 p.m.