The United States and Taiwan signed a trade deal on Thursday aimed at deepening economic relations between both sides — a move that has sparked a warning from Beijing.

The U.S.-Taiwan Initiative on 21st Century Trade looks to boost trade by streamlining customs checks, improving regulatory procedure and establishing anti-corruption measures between the United States and self-governing Taiwan, which China claims as part of its territory.

While Washington and Taipei do not have official diplomatic relations, they maintain unofficial ties through the de facto U.S. embassy on the island, the American Institute in Taiwan.