In order to fulfill the order, those wearing a mask will furthermore be required to wear their mask in such a way that it completely covers their mouth and nose. Face shields and goggles are not permitted as substitutes for masks, and wearing a mask that is either too small or too large can also run afoul of the order.
The order, which was issued in conjunction with an executive order issued by President Biden earlier this week that required all agencies to follow CDC guidance, effectively reverses Trump administration policy, under which the CDC strongly advised the use of masks on all public transportation, but left the determination of whether to issue a binding mandate to that effect to the states and cities that are in charge of those public transportation systems.
The order, which was issued late Friday, was accompanied by a statement from CDC Director Dr. Rochelle P. Walensky, MD, MPH, which encouraged Americans to avoid travel altogether if possible. However, according to Dr. Walensky, "for those who must travel, additional measures are being put in place to help prevent the spread of the virus. Masks are most likely to reduce the spread of COVID-19 when they are widely and consistently used by all people in public settings."
The order is the latest federal mask mandate to be implemented since the beginning of the Biden presidency, following executive orders requiring masks on all federal land (an order which Biden himself promptly violated), as well as an order requiring masks for all interstate travel.