China filed an official protest with the U.S. on Sunday over a defense policy bill that envisions hypothetical military exchanges with Taiwan. China’s foreign ministry took issue with a portion of the $618.7 billion National Defense Authorization Act that “expresses the sense of Congress that [the U.S. Department of Defense] should conduct a program of senior military exchanges between the United States and Taiwan.” Beijing confronted Washington with “stern representations” over the inclusion of Taiwan, stressing that the disputed island-nation is a Chinese territory. While the bill’s mention of Taiwan is not legally binding, China said the mere mention of it represented an interference by the U.S. in Chinese domestic affairs. “We urge the U.S. side to abide by its promises made to China on the Taiwan issue, stop U.S.-Taiwan military contacts and arms sales to Taiwan, to avoid damaging Sino-U.S. ties and peace and stability in the Taiwan Strait,” the ministry’s statement said, according to Reuters. Taiwan has been a point of contention in relations between Washington and Beijing in recent weeks after President-elect Donald Trump angered Chinese leaders by holding a phone conversation with Taiwan President Tsai Ing-wen.