By securing Mr. Pai’s recommendation, the companies cleared a key hurdle toward creating a wireless carrier with more than 125 million customers that would immediately become a strong competitor to AT&T, which has 148 million, and Verizon, which has 118 million.

John Legere, the colorful chief executive of T-Mobile and an active presence on Twitter, would become the leader of a combined company. He has been the deal’s pre-eminent pitchman, lobbying legislators and promoting the merger to his 6.2 million Twitter followers.

“We took some action on those discussions, and we submitted a set of commitments to the F.C.C. around the New T-Mobile to address what we’ve heard,” he said in a statement.

A vote of the agency’s five commissioners is expected in the coming weeks and could fall along party lines. Mr. Pai, a staunch advocate of deregulation, leads the agency’s Republican majority.

Democrats and consumer advocates have previously criticized the proposed transaction, arguing that it would lead to higher prices. Jessica Rosenworcel, a Democratic commissioner, said after Mr. Pai’s announcement that she had “serious doubts” about the deal, citing similar mergers in the airline and drug industries.

“It hasn’t worked out well for consumers,” she added.

The companies are also awaiting the approval of the Justice Department, which is expected to issue a decision on the matter in the coming weeks. The agency’s mandate — to focus on whether such deals harm competition — differs from the F.C.C.’s, potentially posing a greater regulatory obstacle.

In 2011, the Justice Department blocked AT&T’s proposed acquisition of T-Mobile. In that instance, both the Justice Department and the F.C.C. concluded that reducing the number of major wireless carriers from four to three could destroy competition and hurt consumers.