Federal health officials are requiring airlines to gather contact-tracing information on passengers heading to the U.S. who have been in southern Africa in the previous two weeks.

The Centers for Disease Control and Prevention said Wednesday that it issued the latest requirement “to prevent the importation and spread of a communicable disease of public health importance.”

The directive follows President Joe Biden’s order that bars most foreign nationals from entering the U.S. if they have been in southern Africa, where the omicron variant of COVID-19 was first reported. The ban does not apply to American citizens or permanent U.S. residents who have been in those countries, although they must show evidence of a negative test for COVID-19.

Under the CDC order, which was obtained by The Associated Press, airlines will be required to keep information on those passengers for 30 days and give it to the CDC within 24 hours of a request by the health agency.

The information includes a passenger’s full name and date of birth, where they will be staying in the U.S., an email address they check regularly, and main and secondary phone numbers. Airlines will also have to provide the passenger’s flight number, the departure and arrival cities, and their seat number.

The directive, which started with flights on Monday, covers travelers who have recently been in Botswana, Eswatini, Lesotho, Malawi, Mozambique, Namibia, South Africa or Zimbabwe.

So far, United Airlines is maintaining its schedule of five flights a week between Newark, New Jersey, and Johannesburg, South Africa, and planned to resume flights to Cape Town on Wednesday. A spokeswoman said United was following all government requirements for international travel including contact-tracing information.

Delta Air Lines flies three times a week between its home in Atlanta and Johannesburg and, like United, says it has no plans to alter its schedule. A spokesman said Delta will comply with all CDC directives.