While serving as transportation secretary during the Trump administration, Elaine Chao repeatedly used her office staff to help family members who run a shipping business with extensive ties to China, a report released Wednesday by the Transportation Department’s inspector general concluded.

The inspector general referred the matter to the Justice Department in December for possible criminal investigation. But in the weeks before the end of Trump administration, two Justice Department divisions declined to do so.

Ms. Chao, the wife of Senator Mitch McConnell of Kentucky, the Republican leader, announced her resignation on Jan. 7, the day after the Capitol riot. At the time of her departure, an aide to Ms. Chao said her resignation was unrelated to the inspector general’s investigation.

… The investigators did not make a formal finding that Ms. Chao violated ethics rules. But they detailed more than a dozen instances where her office took steps to handle matters related to her father, who built up a New York-based shipping company after immigrating to the United States from Taiwan in the late 1950s, and to her sister, who runs the company now.