In a veiled warning to U.S. President-elect Donald Trump, China’s ambassador to the United States on Wednesday said that China would never bargain with Washington over issues involving its national sovereignty or territorial integrity.

Ambassador Cui Tiankai, speaking to executives of top U.S. companies, said Beijing and Washington needed to work to strengthen their relationship.

“The political foundation of China-U.S. relations should not be undermined. It should be preserved,” Cui said. “And basic norms of international relations should be observed, not ignored, certainly not be seen as something you can trade off. And indeed, national sovereignty and territorial integrity are not bargaining chips. Absolutely not.”

He did not specifically mention Taiwan, nor Trump’s comments last weekend that the United States did not necessarily have to stick to its longstanding policy of recognizing that Taiwan is part of “one China.”

But Cui’s remarks are in line with recent protests from China’s Foreign Ministry, which regards the four-decade “one China” principle as the “political basis” for U.S.-China ties.