Children under the age of 2 and who cannot wear a mask because of a disability are exempt from the order, which takes effect on Monday at 11:59 pm.
The new CDC rule goes beyond an executive order signed by President Joe Biden last week that required the use of face masks on federal properties and during interstate travel.
The CDC said that although it “reserves the right” to enforce the order through criminal penalties, it will be relying on an honor system practiced by passengers.
Airlines, which largely imposed self-imposed masking regulations prior to Biden’s order and the new CDC rule, previously called on the Federal Aviation Administration to issue a federal masking mandate, but the agency refused, noting that it is not a public health agency.
On Saturday morning, the United States surpassed 25 million cases and 436,000 deaths amid the coronavirus pandemic.