This past Wednesday, United published a Scheduling Alert indicting procedures to follow to comply with CDC directives when entering the United States from another country. Some requirements and procedures have been updated.
The CDC requires a negative COVID-19 test, or recovery form, for International travel into the U.S. Working crewmembers, including deadheading crew, are exempt. If deviating from a scheduled deadhead (unless traveling PS0), you will not be able to check-in online. Effective February 17, an exception letter will be available in your content app, in the COVID-19 resources folder, and may be shown to the CSR when deviating from a deadhead or if United has purchased offline tickets on another carrier (for purposes of positioning a crewmember). You will need to check in at the designated check-in area and provide the letter to the CSR so they may complete your flight check-in process.
Traveling for any other reason: to/from training, commuting or pleasure travel require compliance with the CDC requirements, without the exemption.