Senator Elizabeth Warren has made her disagreement with the U.S. Education Department's (ED) handling of Sallie Mae known, warning the agency not to become a "lapdog."

She told the Huffington Post Thursday following ED's decision to renew its contract with Sallie Mae "deeply concerned" her. Sallie Mae is currently under investigation by three agencies for possible borrower rights violations, but was told by the ED their contract to collect federal student loans would be renewed.

"The Department of Education needs to be aggressive in watching out for students, not for profit-making loan servicers," Warren (D-Mass.) said. "They're there for our students, not to help loan servicers make a profit."

A member of the Senate banking and education committees, Warren was also troubled by allegations the ED has yet to recoup $22 million it supposedly gave to Sallie Mae in 2009.

Education Secretary Arne Duncan is also not doing himself any favors with critics who believe his agency is being too soft with the companies who collect repayments of federal student loans. The same companies are also being accused of shady practices that may include violating the rights of their borrowers. As a result, Duncan and the ED have been criticized for not paying close enough attention to them.

Warren wrote Duncan a letter in Sept. raising these concerns and firmly requested he answer to the critics.

"The whole point of the letter was to make sure the Education Department is making it a priority to review its own contracts with an eye toward how Sallie Mae and others are executing on their responsibilities," Warren said. "That's what I'm trying to do."

Stephen Spector, a spokesman for the ED, said Duncan had yet to respond to the letter and Warren said she still has not heard from him.

"Arne Duncan told me about a month ago that he was going to respond within a day or two, and then nothing," she said. "We've been in touch with his staff since then, and they keep saying another couple of days. I've reached the point where I'm not sure what to expect from them."