WASHINGTON — The House Oversight and Reform Committee asked Transportation Secretary Elaine Chao on Monday to turn over documents related to communication with her family’s shipping company as the panel stepped up an investigation into whether any actions taken by Ms. Chao amount to a conflict of interest.

The request by the committee in the Democrat-controlled House relates to actions Ms. Chao has taken that potentially benefited Foremost Group, a New York-based shipping company owned by her family. Foremost has received hundreds of millions of dollars in loan commitments from a bank run by the Chinese government to help build ships that Foremost has purchased from government-owned shipyards there.

The actions by Ms. Chao — including joint public appearances since she became transportation secretary in 2017 with her father, James Chao, who founded the company, and a planned trip to China to meet with government officials there along with her father — have led House investigators to question if she is using her office to try to benefit her family’s financial interests.

“Federal regulations prohibit federal employees from using their public offices for the ‘private gain’” of friends or relatives, said the letter sent on Monday to Ms. Chao by the House investigators, who cited articles that appeared in The New York Times in June and Politico in 2018 that detailed continued ties between Ms. Chao and her family’s company. “Several reports indicate that you have used your official position to benefit Foremost Group, a shipping company owned by your father and sisters that is headquartered in New York and operates a fleet that transports materials to and from China.”