Workers assemble automobiles at a workshop of Shanghai General Motors Company Ltd, Qingdao Branch, on March 1, 2016 in Qingdao, Shandong Province of China.

Shares of General Motors fell 3 percent Wednesday after a report said China will penalize an unnamed U.S. automaker for monopolistic behavior.

Shares of American automaker Ford Motor declined nearly 1.9 percent on the day.

Investigators found the unnamed U.S. automaker instructed distributors to fix prices starting back in 2014, the official China Daily newspaper reported, citing Zhang Handong, director of the National Development and Reform Commission's price supervision bureau.

The report said it would be the second penalty issued by the NDRC this month.

On Tuesday, GM asked the Supreme Court to overturn an earlier ruling that its 2009 bankruptcy filing did not shield it from lawsuits related to its faulty ignition switches.

General Motor's stock is up more than 5 percent year to date.