The top official at the US communications regulator on Monday announced his support for the proposed $26 billion merger between telecoms firms Sprint and T-Mobile.
The decision raises the chances the merger will win final approval from federal authorities.
But the companies still face an anti-trust review by the US Department of Justice, which media reports say fears declining market competition if the deal goes through.
Ajit Pai, chairman of the Federal Communications Commission, said both companies had promised his agency they would offer a next-generation 5G network to 99 percent of Americans within six years of completing the deal while also expanding access to mobile broadband.
The companies have agreed not to raise rates for three years and will divest from the Sprint subsidiary Boost Mobile.