Edward Lampert speaks during a news conference to announce the merger of Kmart and Sears in New York, Nov. 17, 2004. Gregory Bull | AP

Presidential candidate Sen. Elizabeth Warren and Rep. Alexandria Ocasio-Cortez sent a letter to Sears' former Chairman and CEO Eddie Lampert lambasting him for efforts to avoid repaying Sears for $43 million in severance fees. Lampert bought Sears out of bankruptcy last year through an affiliate of his hedge fund ESL Investments, Transform Holdco, after years of declines under his leadership as CEO and chairman. The deal, which saved the company from liquidation, also promised that Lampert would reimburse Sears severance costs for workers who lost a job in bankruptcy. Sears and Lampert have since sparred over what each party believes they are owed by the other as part of the deal. Lampert said in court filings that Sears fell short of what it owes him. To help make up the loss, he is requesting approval from the bankruptcy court judge to not pay back Sears for $43 million in severance fees. The two parties, though, now estimate severance costs to be closer to $20 million. Still, a spokesperson for Transform told CNBC that severance owed has already been paid. He stated, in part, "To be clear, employees of old Sears who lost their jobs during bankruptcy have already received their severance payments." He added, "Transform agreed to reimburse Old Sears for these severance payments in exchange for the receipt of certain assets. Old Sears has admitted that $55 million of those assets have not been transferred to Transform, although Transform believes the amount is larger. As a result, Transform is not obligated to reimburse Old Sears for having made the severance payments."

Still, in a letter sent Thursday, Warren, D-Mass., and Ocasio-Cortez, D-N.Y., lashed out at Lampert. "The failure to make those payments would amount to a broken promise on your part, and a betrayal of hard-working Sears employees — some of whom have worked at the company for decades — who are relying on the severance that they have been promised to pay rent, care for children, and put food on the table," they said. The two referred to a written exchange between Lampert and Warren earlier this year in which the senator inquired about Lampert's plan to buy Sears' out of bankruptcy and the retailers' viability under his ownership. In Lampert's response, dated Feb. 19, he defended his management of Sears and assured Warren that his deal to buy the retailer would guarantee severance payments to employees who lost their job after it filed bankruptcy on Oct. 15 and did not rejoin the company. "But for the sale to ESL, these employees would be getting nothing," Lampert wrote. Spokespeople for Warren and Ocasio-Cortez couldn't immediately be reached to comment on Transform's claim that severance was already paid to the workers. An attorney who represents Sears also wasn't immediately available.

Mediation isn't free