Transportation Secretary Sean Duffy sharply criticized Ford Motor's business with Chinese automotive firms, saying the company's "reliance on technologies of foreign adversaries" isn't sustainable for America.

"While DOT recognizes the intense competitive pressures of the global market, the company's recent strategic decisions paint a troubling picture of a foundational American brand actively intertwining its future with Chinese state-backed enterprises," Duffy said in a letter to Ford Chief Executive Jim Farley dated last Thursday. The letter was made public by the Transportation Department on Tuesday.

The letter marks the latest rebuke of Ford's ongoing business deals with Chinese firms, which have drawn the ire of Republicans and Democrats in Congress.

Duffy singled out Ford's arrangement to license battery technology from the Chinese firm CATL, as well as a recently announced joint venture with the Chinese automaker Geely in Europe.

Duffy also called the manufacturing of Lincoln vehicles in China for the U.S. market "unacceptable."

Ford didn't immediately respond to a request for comment.