(Reuters) – U.S. wireless carriers T-Mobile US Inc and Sprint Corp are considering divesting wireless spectrum, according to two sources familiar with the matter, as the companies work to gain regulatory approval for their merger.

The $26-billion deal won support from the U.S. Federal Communications Commission last week, but still needs approval from the U.S. Department of Justice, which is looking at the merger on antitrust grounds.

It was not immediately clear what the sale process would be for the spectrum, or airwaves that carry data. Bloomberg reported earlier on Thursday that T-Mobile and Sprint were considering divesting spectrum back to the government, which would then sell it to help establish a fourth carrier, citing sources.

The two carriers had previously offered concessions to get the merger approved, which includes selling prepaid brand Boost Mobile, in order to reduce the combined company’s market share in the prepaid wireless business.

But some analysts and consumer advocates have raised concerns that wireless prices could rise if the merger is approved, which would leave the U.S. with three carriers from four.