On January 21, 2021, President Biden signed an executive order directing federal agencies to “require masks to be worn in compliance with CDC guidelines” in various modes of transportation, including public transportation. Today, this order was extended through September 13, 2021.
Security Directive (SD) 1582/84-21-01A applies to passenger railroads, intercity bus services, and public transportation.
The order states that it applies to travel in or on:
All questions regarding the security directive can be sent to the TSA via TSA-Surface@tsa.dhs.gov