Senator Elizabeth Warren blasted Jamie Dimon for reviving a policy that pushes JPMorgan Chase & Co.’s credit-card customers into arbitration to resolve disputes instead of the courts.

“We write to express our strong concern with reports that Chase has decided to reverse course and to urge you to reconsider your plans to resume exploiting its customers,” the Massachusetts Democrat said in a letter to Dimon, the chief executive officer of the biggest U.S. bank. Representative Jesus “Chuy” Garcia, an Illinois Democrat, also signed the letter, which was dated Thursday.

Warren, who has advocated breaking up big banks and other corporate giants, said arbitration lets companies “get away with scamming large numbers of customers out of relatively small amounts of money.”

Banks say mandatory arbitration is faster and cheaper for the public than litigation, and JPMorgan called it “standard practice” for the industry when it announced the switch earlier this month. The New York-based company’s customers can opt out of mandatory arbitration if they mail a written rejection notice by Aug. 9.

JPMorgan declined to comment on Warren’s letter.

It’s not the first time Warren and Dimon have sparred. Four years ago, Dimon expressed doubts about the Senator’s understanding of the global banking system, though he said he agreed with some of her concerns about risks. Warren later shot back, saying bankers dislike her because she knows too much about how their companies work, not too little.