More: Investigators at the Commerce Department were deep into a monthslong investigation of a Singaporean company that they suspected of smuggling Nvidia's artificial intelligence chips into China when their work came to a sudden halt late last year.

The investigation centered on Megaspeed, a data center company led by an executive who U.S. officials now believe to be a Chinese spy who had a relationship with Nvidia's chief executive, Jensen Huang.

But the case was abruptly transferred to the Justice Department last year. The shift came after Commerce Department investigators working on the case received an email from Nvidia's general counsel seeking information about the inquiry into Megaspeed.

It is not necessarily unusual for Commerce Department agents working on a case to speak with a company's representatives about issues involving their firm. But what was unusual was the content of the message. Tim Teter, Nvidia's general counsel, said that Jeff Kessler, a top official at the department, had given Nvidia permission to reach out about the case.

The agents were alarmed that Nvidia had invoked the name of Mr. Kessler, their superior, who was nominated to his role by President Trump. Some viewed Mr. Kessler's interaction with Nvidia as violating government procedure and potentially tainting the case, according to current and former government officials and others familiar with the incident.

It is not clear what led to Mr. Teter's outreach to the department, but the recent revelations about Mr. Huang's acknowledged affair with a Megaspeed executive have only intensified scrutiny of Nvidia's role in influencing policy on chip sales to China. The New York Times reported last month that the U.S. government had concluded that Huang Le, or Alice Huang, a top executive at the firm, was a spy working on behalf of the Chinese government.