The CDC has provided updated information for both domestic and international travelers regarding COVID-19:
Domestic Travel During COVID-19
Information for People Traveling by Air and Land within the United States and U.S. Territories
https://www.cdc.gov/coronavirus/2019-ncov/travelers/travel-during-covid19.html
International Travel to and from the United States
CDC Guidance on U.S Citizens, U.S. Nationals, U.S. Lawful Permanent Residents, and Immigrants: https://www.cdc.gov/coronavirus/2019-ncov/travelers/international-travel-during-covid19.html
Airline partners’ COVID-19 updates:
Each airline has implemented different procedures in response to COVID-19, such as plexiglass shields at ticketing counters, seating adjustments, and mask requirements for boarding aircraft. Check with your airline for more information. Airline contact information and COVID-19 updates can be found on the Airlines at MEM page.