The Justice Department is leaning against approving T-Mobile U.S. Inc.¡¯s proposed takeover of Sprint Corp., according to a source familiar with the review, even after the companies won the backing of the chairman of the Federal Communications Commission.

The remedies proposed by the wireless carriers Monday don¡¯t go far enough to resolve the department¡¯s concerns that the deal risks harming competition, said the source, who asked not to be named because the investigation is confidential.

Opposition to the deal by the Justice Department¡¯s antitrust chief, Makan Delrahim, would mark a rare break with the FCC. The two agencies work side by side on merger reviews and typically emerge on the same page about whether to approve deals.