United States Senator Tom Cotton has called on the Pentagon to clarify whether Microsoft has employed Chinese engineers to help maintain U.S. military cloud computing systems, citing national security concerns raised by a recent investigative report.

In a letter to Defense Secretary Pete Hegseth, the Arkansas Republican—who chairs the Senate Intelligence Committee and sits on the Armed Services Committee—requested detailed information on Microsoft’s contractor practices following a report by ProPublica.

The investigation revealed that Microsoft used engineers based in China to work on sensitive military systems under the supervision of U.S. “digital escorts”—security-cleared subcontractors who reportedly lacked the technical expertise to detect cybersecurity risks.

Cotton urged the Department of Defense to provide a full list of contractors using Chinese personnel and to explain how digital escorts are trained to identify potentially suspicious activity.

“The U.S. government recognizes that China’s cyber capabilities pose one of the most aggressive and dangerous threats to the United States,” Cotton wrote. “The military must guard against all potential threats within its supply chain, including those from subcontractors.”

The company, a major U.S. defense contractor, has previously been targeted by both Chinese and Russian hackers.

Cotton’s inquiry highlights growing concerns in Washington over the role of foreign engineers in U.S. defense systems amid broader fears of supply chain vulnerabilities and cyber espionage.

The senator’s letter adds further pressure on the Pentagon to tighten oversight of technology contractors and subcontractors in critical national security projects.