EMS-FORSTER-PRODUCTIONS | DigitalVision | Getty ImagesWASHINGTON — The U.S. Centers for Disease Control and Prevention said Wednesday that it requested the Justice Department to proceed with an appeal of a ruling that lifted a travel mask mandate.”CDC believes this is a lawful order, well within CDC’s legal authority to protect public health. CDC continues to recommend that people wear masks in all indoor public transportation settings,” the agency wrote in a statement adding that it will continue to monitor public health conditions to “determine whether such an order remains necessary.”The Department of Justice said in a statement that it filed a notice of appeal in the case involving Health Freedom Defense Fund, Inc., et al., versus Biden, et al. On Monday, U.S. District Judge Kathryn Kimball Mizelle ruled in that case that the travel mask mandate was unlawful. The CDC’s mask mandate was enacted in February 2021 and recently extended through May 3.The new appeal is largely expected to have no immediate effect given that the Justice Department has not yet made an attempt to block Mizelle’s order. The appeal process is slated to unfold over a number of months.On the heels of Mizelle’s decision, the White House said the Transportation Security Administration will not enforce the rule on public transport while the ruling is reviewed.Some transportation companies, such as the airlines United and Delta and the railroad operator Amtrak, were quick to announce Monday evening that wearing masks was now optional for passengers and employees using their travel services.CNBC’s Kevin Breuninger contributed to this report.This story is developing. Please check back for updates.