Sen. Elizabeth Warren (D-Mass.) asks a question during a Senate Banking Committee hearing in Washington on Feb. 11. (Andrew Harrer/Bloomberg)

Sen. Elizabeth Warren (D-Mass.) is ratcheting up pressure on the Department of Education to cut ties with Navient Solutions, one of the companies that collects and applies federal student loan payments on behalf of the government.

The progressive leader sent a letter to the department’s chief operating officer, James Runcie, this week, raising concerns about the student loan servicer’s “extravagant and increasing lobbying expenditures.” Warren said her staff found that in addition to the $710,000 that Navient spent lobbying Congress on its own, the company paid outside firms an additional $155,000 to lobby on its behalf in the first three months of the year. Navient, she said, has spent a total of $3.7 million on lobbying since 2015, and almost $24 million since 2010.

“I am mystified by the scope of these expenditures,” Warren wrote. “Navient should be focused on and investing in improving its abysmal student loan servicing operations, not lobbying Congress and the administration in search of sweetheart deals.”

Officials at Navient say the lobbying expenses Warren lists are inaccurate, and the money the company spent on lobbying has actually declined by 30 percent year over year. They say Navient has been lobbying Congress to streamline student loan repayment options and default rehabilitation, among other things to help borrowers.

“Navient has a long public and well-documented record of assisting borrowers to successfully manage their student loans,” said Patricia Christel, a spokeswoman for Navient. “In fact, 300,000 fewer borrowers would have defaulted last year if other servicers performed at our level.”

Warren contends that Navient has a less than stellar track record with borrowers, as evidenced by a series of settlements and investigations by the Department of Justice, the Federal Deposit Insurance Corp. and the Consumer Financial Protection Bureau for allegedly mistreating consumers.

A coalition of state attorneys general, led by Illinois’s top prosecutor Lisa Madigan, is also alleging that Navient violated state consumer protection laws by rewarding call center workers for rushing borrowers off the phone, an investigation first reported by the Huffington Post. Warren cited the latest investigation and others in her letter, questioning the department’s decision to extend Navient’s contract, worth more than $100 million a year, through 2019.

“While the Education Department is paying Navient hundreds of millions of dollars to service student loans, the company continues to evade responsibility for past failures,” Warren wrote, referencing a decade-old investigation by the department’s inspector general.

The inspector general caught several private lenders, including Navient’s former sister company Sallie Mae and Nelnet, overcharging the government by tens of millions of dollars. Nelnet was never required to return the $278 million it received, nor has Navient, which assumed Sallie Mae’s liabilities when the companies parted ways, handed back the $22.3 million it owes.

Officials at Navient say the company remains in active discussions with the department on the matter and has the right to appeal the inspector general’s audit. Warren chided the department for continuously extending the deadline for the company’s appeal, effectively letting Navient off the hook for stealing from taxpayers.

“The $24 million that Navient has spent on lobbying in the last six years is enough to repay the full $22 million in overpayments — with almost $2 million left over to provide additional relief to borrowers,” the senator wrote. “But this has not happened. Instead, Navient has been allowed to spend these funds lobbying Congress and the administration in search of additional perks.”

Warren has been relentless in her criticism of Navient since the Justice Department and FDIC accused the company in 2014 of unlawfully charging nearly 78,000 active-duty service members high interest rates on student loans. She has challenged the department’s decision to do business with the company and called for an investigation into an agency report minimizing Navient’s alleged mistreatment of the troops.

Although Warren has not gone as far as to ask the department to end its contract with Navient, she is asking the agency to consider the company’s troubled history before awarding it any new contracts. In the letter, she called on the department to “keep the interests of students and their families, not Navient and its lobbyists, first and foremost” in making contracting decisions.

Navient spokeswoman Christel argues that “student loan servicing decisions should be based on facts not politics.”

She added: “An assessment of the facts would make clear that Navient delivers better results than any other servicer. We have invited the senator to visit our center to witness firsthand the work we do.”

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