Turkish Airlines and Lot Polish Airlines have signed a letter of understanding that could lead to a joint venture,

the carriers announced Thursday. The letter indicates “a major expansion of commercial ties,” though they have not decided the final model of cooperation. The carriers, both Star Alliance members, are expanding their codesharing agreements, as well. They have codeshared on flights between their main hubs in Istanbul and Warsaw since 2000, expanded to a few other key cities in 2014 and will add codeshares on domestic flights within Turkey and Poland, as well as flights to destinations in Africa, the Middle East and Asia.