Democratic presidential candidate Elizabeth Warren gestures as she speaks during a campaign stop at George Mason University in Fairfax, Virginia on May 16, 2019.

Presidential candidate Sen. Elizabeth Warren, D-Mass., and Rep. Alexandria Ocasio-Cortez, D-N.Y., are targeting Treasury Secretary Steven Mnuchin, raising questions about his time on Sears Holdings' board of directors and his relationship with the troubled company's former CEO, Eddie Lampert.

Mnuchin, who was Lampert's roommate at Yale University, was on the Sears board until December 2016, after President-elect Donald Trump picked him to join the incoming Cabinet.

Under Lampert, who led Sears from 2013 to 2018, the company closed more than 3,500 stores, shed some of its most valuable assets, including Lands' End, and laid off thousands. Sears filed for bankruptcy in October. Lampert bought Sears through an affiliate of his hedge fund ESL Investments, saving it from total liquidation.

In a four-page letter sent Thursday morning, Warren and Ocasio-Cortez asked Mnuchin a series of questions about his advisory role in Lampert's decisions.

In a video on Twitter announcing the letter to Mnuchin, Ocasio-Cortez criticized the secretary as "a walking example of what happens when rich and powerful people put other rich and powerful people into power."

Workers "deserve a Treasury secretary who fights for them," Warren said in the video, "not someone who spent a decade raking in cash for himself at the expense of hundreds of thousands of Sears employees."

Warren TWEET Video

The Treasury Department did not immediately respond to CNBC's request for comment on the letter from Warren and Ocasio-Cortez. ESL declined to comment.