T-Mobile US Inc. suffered a significant setback in its bid for regulatory approval of its takeover of Sprint Corp. after failing to win over the U.S. Justice Department with a remedy package, putting pressure on the companies to offer more concessions.

The wireless carriers could try to sell additional assets to resolve the department’s concerns that the deal would harm competition. The question is whether there’s anything the companies can propose, like selling airwaves or another business unit, that will sway the department’s antitrust boss, Makan Delrahim.

“I don’t see how any concessions short of somehow helping to set up a new fourth competitor could make this deal palatable to DOJ,” said Gigi Sohn, an opponent of the merger and a former aide to a Democratic chairman of the Federal Communications Commission.

More at Bloomberg.