Sen. Richard Blumenthal, D-Conn., wants an investigation into Commerce Secretary Wilbur Ross’s shared business interests with members of Russian President Vladimir Putin’s immediate family.

“Why do so many Trump associates have such trouble disclosing relationships with Russia?” Blumenthal tweeted Sunday. “In concealing an ongoing financial relationship w/ Russian oligarchs, Sec. Ross misled me, Senate Commerce Committee & the American people. Inexcusable and intolerable. Americans are owed answers on this Cabinet’s troubling failure to disclosure links to Russian interests.

“With Wilbur Ross revelations, question must be asked — whose interests come first in this Administration? Only after a thorough investigation can Americans be sure Secretary Ross really has their best interests at heart.”

A leak of 7 million internal documents from a law firm in Bermuda, dubbed the “Paradise Papers,” shed light on Ross’s business interests.

The Commerce secretary has a stake in Navigator Holdings, a shipping company partially owned by his former investment firm, WL Ross & Co.

Navigator Holdings has a partnership with Sibur, a Russian energy company controlled by Putin’s son-in-law. One of the firm’s owners, Gennady Timchenko, is prohibited from entering the U.S. and is named on a sanctions list from the Treasury Department.

Ross retained his stake in Navigator after he was tapped to serve as President Trump’s secretary of Commerce.