The U.S. Department of Justice said Tuesday that it will appeal a court ruling which struck down the federal government's mask mandate for travelers, but only if the U.S. Centers for Disease Control and Prevention determines the mandate is still necessary to protect public health.

"The Department continues to believe that the order requiring masking in the transportation corridor is a valid exercise of the authority Congress has given CDC to protect the public health. That is an important authority the Department will continue to work to preserve," it said in a statement.