CMMC Practice MP.3.125
Implement cryptographic mechanisms to protect the confidentiality of CUI stored on digital media during transport unless otherwise protected by alternative physical safeguards.
Bold Coast Security Guidance
We alluding to encrypting data in MP.3.124 as a key control for transporting media, and it is codified in this practice. Your organization should take into consideration all backup tapes, USB drives, and other forms of digital media.
Laptops and other mobile devices are addressed in another practice (AC.3.022), but the same thought process is going on here.
DRAFT NIST SP 800-171 R2
This requirement applies to portable storage devices (e.g., USB memory sticks, digital video disks, compact disks, external or removable hard disk drives).