American Airlines and British Airways are trying again.

The airlines recently filed yet another request for a code-sharing agreement, after having been turned down twice due to opposition from the U.S. Department of Transportation.

American wants to sell British Airways’ flights from the United Kingdom to Ireland, continental Europe, Africa, the Middle East and Asia, while British Airways seeks to sell American flights from gateway cities such as New York to other points within the United States, Mexico, the Caribbean and Latin America.

Under code-sharing agreements, an airline that sells a ticket on another carrier receives a portion of the fare.

The Transportation Department has 28 days to approve or reject the request. If regulators approve, the airlines may start selling tickets on each other’s flights as early as January.