CDC issued an order requiring "people to wear masks while on conveyances and at transportation hubs," and directing conveyance officers to enforce its provisions.

Here's the order: https://www.cdc.gov/quarantine/pdf/Mask-Order-CDC_GMTF_01-29-21-p.pdf

Here's the law they cite as their authority: https://www.law.cornell.edu/uscode/text/42/264

Problematically, the law authorizes the Surgeon General, with the approval of the Secretary, to issue orders, not the CDC, and ONLY with regards to movement across the U.S. borders or between U.S. states, and it allows the detention/examination ONLY of persons reasonably believed to be infected AND in a communicable/precommunicable state of that infection.

It provides no authority for the CDC to do ANYTHING.

It provides no authority for ANYONE to require masks.

It provides no authority for ANYONE to require ANYTHING for someone not reasonably believed to be in a qualifying state of infection.

I.e., the CDC's order is entirely without legal authority and, in acting under it, the CDC is abusing their own official office to illegally deprive U.S. citizens of their rights, under color of law, and placing any company or office which seeks to carry out the order in legal jeopardy.