Delta Air Lines CEO Ed Bastian on Tuesday asked the Centers for Disease Control and Prevention to halve its recommended quarantine time for vaccinated people who contract Covid-19, saying the current isolation period could negatively affect the airline’s operations.

Bastian wrote to CDC Director Rochelle Walensky proposing a five-day recommended quarantine period for fully vaccinated individuals who contract Covid. The existing recommendation calls for a 10-day period of isolation.

“Our employees represent an essential workforce to enable Americans who need to travel domestically and internationally,” wrote Bastian, along with the airline’s chief health officer Henry Ting and medical advisor Carlos del Rio. “With the rapid spread of the omicron variant, the 10-day isolation for those who are fully vaccinated may significantly impact our workforce and operations.”

The letter comes as Covid cases spike and the heavily mutated omicron variant spreads rapidly, straining testing supplies ahead of the year-end holidays.

Bastian, del Rio and Ting argued the CDC guidance was developed “in 2020 when the pandemic was in a different phase without effective vaccines and treatments.” The executives suggested individuals could end the isolation period earlier on the condition of a negative Covid test.

“As part of this policy change, we would be interested to partner with CDC and collect empirical data,” they wrote in the letter, which Delta posted on its website and which was earlier reported by Reuters. The CDC didn’t immediately return a request for comment.

Delta said that about 90% of its staff is fully vaccinated and noted that all airline personnel, like travelers, are required to wear masks at airports and on commercial airplanes.