The Wall Street Journal reported Sunday that a grand jury in Washington, D.C., issued a subpoena for documents last week to at least one person involved in the development of the 737 Max.
The Journal reported that the Justice Department inquiry involves a prosecutor in the fraud division, which has previously brought cases against manufacturers over safety issues.
The Department of Transportation and Boeing did not immediately respond to a request for comment from The Hill, but Boeing declined to comment to the Journal regarding legal matters or government inquiries.
The newspaper reported earlier Sunday that the Department of Transportation's inspector general is looking at the Federal Aviation Administration (FAA) over an anti-stall system that is a focus of the investigation into a fatal Lion Air crash last October that involved a 737 Max 8. It's unclear if the subpoena is related to that internal investigation.
Boeing and the FAA have been under heightened scrutiny after the crash of an Ethiopian Airlines 737 Max 8 earlier this month that killed all 157 people aboard. The company and the agency both maintained the planes were safe in the days after the crash, even as multiple countries grounded the planes.
President Trump announced last Wednesday that 737 Max 8 and 9 planes would be grounded in the U.S. pending an investigation into the causes of the two crashes. The U.S. was the final major country to ground the planes, and the decision came amid mounting pressure from lawmakers.