President Donald Trump on Friday blocked the $3 million acquisition of U.S. aerospace and defense specialist Emcore by photonics firm HieFo Corp, citing national security concerns linked to China.

In an executive order released by the White House, Trump stated that HieFo was “controlled by a citizen of the People’s Republic of China” and said the 2024 acquisition of Emcore’s businesses could lead the company to “take action that threatens to impair the national security of the United States.” The order did not identify the individual or provide further details on the security concerns.

Trump’s directive formally prohibits the transaction and requires HieFo to “divest all interests and rights in the Emcore Assets, wherever located,” within 180 days.

The Treasury Department confirmed that the Committee on Foreign Investment in the United States (CFIUS) had identified a national security risk during its review of the deal, though the department did not elaborate on the specifics of the threat.

HieFo and Emcore did not immediately respond to requests for comment, and no statements were posted on their websites as of late Friday.

Emcore, which was publicly traded at the time of the sale and later taken private, previously stated that HieFo had purchased its chips business and indium-phosphide wafer-fabrication operations for $2.92 million. HieFo said the company was co-founded by Genzao Zhang, a former Emcore vice president of engineering, and Harry Moore, a former senior sales director at Emcore according to his LinkedIn profile.