US Senator Elizabeth Warren sent a letter to regulators Wednesday expressing concerns about underwriting standards in the leveraged loan market, which she says could pose serious risks to the economy.

In the letter, Warren questioned regulators on what their agencies’ plans are to address what she describes as “growing risks” in the leveraged lending market as well as proposed changes to rules governing the Collateralized Loan Obligation (CLO) market, the largest buyers of leveraged loans. She requested responses by December 11.