Transportation Secretary Sean Duffy is accusing Ford Motor Co. of becoming too dependent on Chinese companies, warning CEO Jim Farley that the automaker’s business ties to China threaten U.S. national security and American manufacturing.

In a letter sent Tuesday to Farley and obtained by FOX Business, Duffy criticized Ford’s growing reliance on Chinese technology and manufacturing partnerships, arguing that the strategy raises national and economic security concerns.

The letter marks one of the Trump administration’s strongest public rebukes of a major American automaker over its business relationships with China.

“I am writing to express the profound concern of the U.S. Department of Transportation (DOT) regarding the strategic trajectory of Ford Motor Company,” Duffy wrote, adding that the company’s recent decisions “paint a troubling picture of a foundational American brand actively intertwining its future with Chinese state-backed enterprises.”

Administration officials argue the concerns are twofold: that Chinese law can require companies to provide the government access to proprietary and customer data, creating potential national security risks, and that increased reliance on Chinese manufacturing comes at the expense of American workers.

Duffy pointed to several examples in the letter, including Ford’s continued use of licensed battery technology from Chinese manufacturer CATL at its BlueOval Battery Park in Marshall, Michigan; the company’s joint venture with Chinese-owned Geely in Spain; reported discussions with BYD over hybrid vehicle components; and the company’s delayed plans to reshore Lincoln models such as the Nautilus, which Duffy said could extend until 2030.

He argued those moves deepen Ford’s reliance on Chinese supply chains while helping strategic competitors expand their influence in the global auto industry.

“When a company intentionally chooses to deepen operational dependencies on strategic competitors, it fails to act as the reliable partner the American public and this DOT require,” Duffy wrote.

Duffy also urged Ford to reduce its dependence on foreign technology.

“Iconic American companies, like Ford, are also expected to out-innovate competitors,” he wrote. “To that end, they need to chart clear paths to technological self-reliance.”

The letter comes as lawmakers and the auto industry have pushed for tighter restrictions on Chinese involvement in the U.S. automotive market.

In July, the Senate Commerce, Science and Transportation Committee approved bipartisan legislation that would ban the import, sale and operation of vehicles manufactured by companies designated as foreign entities of concern, including firms based in China. The measure would also prohibit certain connected vehicle technologies developed by those countries.

Separately, the Alliance for Automotive Innovation urged congressional leaders in September to enact a permanent ban on Chinese-made vehicles in the United States.

Ford did not immediately respond to FOX Business’ request for comment.