Posting from the CDC website:
To reduce introduction and spread of new variants of SARS-CoV-2, CDC issued an Order pdf icon[PDF – 9 pages] effective January 26, 2021. It requires all air passengers arriving to the US from a foreign country to get tested for COVID-19 infection no more than 3 days before their flight departs and to provide proof of the negative result or documentation of having recovered from COVID-19 to the airline before boarding the flight. For more information on this testing requirement, see the Frequently Asked Questions. https://www.cdc.gov/coronavirus/2019-ncov/travelers/testing-international-air-travelers.html