China could slap a penalty to unnamed US automakers for monopolistic behavior, a senior Chinese official warned on Wednesday in an interview with China Daily.

"The penalty comes as authorities work to step up against oversight and expand the industries they scrutinize in order to promote fair market," Zhang Handong, the director of the National Development and Reform Commission (NDRC)'s price supervision bureau, said.

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Following the warning, shares of US companies including General Motors and Ford Motor Co. dropped on Wednesday. GM shares plunged 2.28 percent to $36.51, while Ford fell 0.55 percent, the Financial Buzz noted.

The official, however, did not identify the car manufacturers and divulge the size of the penalty.

Meanwhile, Mark Turby, the chief spokesman of Ford's Asia-Pacific operations, said "We are unaware of the issue."

GM, on the other hand, said it "fully respects local laws and regulations wherever we operate. We do not comment on media speculation."

The warning came following US President-elect Donald Trump's comment on the decades-long US policy of acknowledging Taiwan as part of "One China."

"This action is just a hint as to how much power China wields," Michael Dunnes, president of Dunne Automotive, told Financial Buzz. "A small fine of several million dollars is likely. The message is, 'If you want to play, we can play'."

However, sources told the Newsweek that Chinese officials have already been probing on several automakers' pricing practices even before Trump's controversial comment. China has been utilizing its antitrust laws not only to monitor foreign firms' performance but also protect its local brands, UPI noted.

Tagsprice-fixing, China antitrust law, US car manufacturers in China