The DOT inquiry was launched after a new Boeing 737 Max 8 operated by Indonesia's Lion Air crashed into the Java Sea in October, according to the Journal, which cited people familiar with the inquiry. All 189 people aboard died.
Five months later, on March 10, a second Boeing 737 Max 8 plane crashed shortly after takeoff, killing all 157 people on the Ethiopian Airlines plane. Ethiopian Transport Minister Dagmawit Moges said Sunday that preliminary data retrieved from the plane's flight data recorder showed "a clear similarity" with the Indonesian crash.
The Journal reported in an update to the article that a grand jury in Washington issued a broad subpoena one day after the Ethiopian Airlines crash to at least one person involved in the development of the Boeing 737 Max. The subpoena, which reportedly involves a prosecutor from the Justice Department, was said to seek relevant documents, such as emails and other messages.
It is not clear whether the probe by the Justice Department is related to the DOT's investigation, according to the Journal report. The Justice Department did not immediately respond to CNBC's request for comment, sent outside U.S. office hours.
WATCH: Why Airbus and Boeing dominate 99% of the large plane market
Shares of Boeing, a component of the Dow Jones Industrial Average, rose 1.52 percent to $378.99 on Friday but have fallen sharply from their 52-week high of $446.01 reached earlier this month. They were down more than 2 percent in Monday's premarket.
The DOT inquiry is concentrated on a flight safety system suspected of playing a role in the fatal crash in Indonesia, the Journal reported. The WSJ reported in November that Boeing failed to warn the airline industry about a potentially dangerous feature in its new flight-control system.
When contacted for comment on the Journal report, a Federal Aviation Administration spokesman referred CNBC to the DOT. The Transportation Department did not immediately reply to CNBC's request for comment, which was sent outside U.S. office hours.
Editor's note: This story was revised to reflect the Journal's updated characterization of the Transportation Department's inquiry.