An angry China slammed President Trump’s threat on Monday to cut off trade with countries that deal with North Korea, as “unacceptable” and “unfair.” As a reminder, following Sunday’s nuclear test by North Korea, Trump threatened to increase economic sanctions and halt trade with any country doing business with North Korea, a threat he has used before without following through. That list would include China, the U.S.’s biggest trading partner, which accounted for about a sixth of its overseas commerce.

The United States is considering, in addition to other options, stopping all trade with any country doing business with North Korea.

— Donald J. Trump (@realDonaldTrump) September 3, 2017

The comments were seen as a not-so-veiled warning to China, Kim’s closest ally and commercial partner, and led to a prompt response by China’s Foreign Ministry spokesman Geng Shuang who classified Trump’s comments as “definitely unacceptable.”

“What is definitely unacceptable to us is a situation in which on the one hand we work to resolve this issue peacefully but on the other hand our own interests are subject to sanctions and jeopardized,” Geng said at a regular briefing in Beijing, according to the Associated Press.

Of course, a full-blown trade war would have adverse consequences for both nations: China would be drastically affected if the US were to cut trade ties with it, as the United States imports goods worth about $40 billion a month. Of course, such a move would have devastating, and inflationary, consequences on the US as supply chains are forced to find alternatives to China.

When asked on Monday whether Beijing would support tougher UN sanctions including cutting off oil supplies to North Korea, Geng said that whatever happened would depend on discussions among UN Security Council members. He added that China – a permanent member of the UN’s Security Council with the power to veto UN actions – would take part in a “responsible and reconstructive way.”