Here you go:
https://www.transportation.gov/safet...federal%20law.
Here's the relevant part for international flights:
"This Order must be followed by all passengers on public conveyances (e.g., airplanes, ships, ferries, trains, subways, buses, taxis, rideshares) traveling
into, within,
or out of the United States as well as conveyance operators (e.g., crew, drivers, conductors, and other workers involved in the operation of conveyances)." (Emphasis added.)
No airline -- foreign or domestic -- is forced to fly into or out of the United States. If a foreign airline chooses to serve the United States, it must comply with U.S. laws, rules, and regulations, including the emergency order issued by the U.S. Centers for Disease Control and Prevention.