The U.S. Centers for Disease Control and Prevention has ordered airlines to provide the names of passengers arriving in the U.S. who have traveled to southern Africa in recent days as it assesses the potential spread of the omicron variant of the coronavirus.

The CDC told carriers that they must provide the information to allow for contact tracing in a letter sent Tuesday, the agency said in a press release. The airlines had been told to collect potential contact-tracing data in an order last October but weren’t required to submit it to the agency.

"CDC is issuing this directive to prevent the importation and spread of a communicable disease of public health importance,” it said in the release.