A Chinese state-run newspaper reported this week that regulators will soon fine an unnamed U.S. automaker for "monopolistic behavior." A separate report from Bloomberg News suggestedGM (GM) is the target, which drove down its stock price.

The Chinese newspaper report did not elaborate on the allegations, but China has launched price-fixing investigations into other automakers in recent years and imposed multi-million-dollar fines.

The new threat comes after President-elect Donald Trump rattled China by accepting a congratulatory phone call from the president of Taiwan and questioned the longstanding U.S. position that Taiwan is part of "one China."

Trump has also threatened to slap tariffs of 45% on Chinese imports to the United States to correct a trade imbalance. Chinese retaliation against American companies is not out of the question.

China is by far the largest auto market in the world, and sales are rising quickly. In all, Chinese consumers bought nearly 24 million vehicles last year, up from about 16 million just six years ago, according to the data providers Euromonitor and JATO.

GM (GM) sales in particular are on a record run there. The company delivered 3.4 million cars in China in the first 11 months of the year, up 8.5% from the same period last year. GM sells more cars to Chinese consumers than Americans.