In a letter to U.S. Treasury Secretary Jack Lew, Sen. Sherrod Brown (D-Ohio) and Sen. Elizabeth Warren (D-Mass.) called upon the Treasury to investigate whether any U.S. or U.S.-linked entities were involved in the illicit activities found in the Panama Papers.

According to leaked internal records, Mossack Fonseca & Co. helped clients create shell companies to hide assets, launder money or evade taxes.

In the April 7 letter, the senators wrote, "The reported involvement of U.S. or U.S.-linked institutions and individuals in what may have been efforts to enable international money laundering and tax evasion raises important questions about the susceptibility of the U.S. financial system to money laundering, terrorist financing and other illicit enterprises."