The Senate will hold an antitrust hearing on the proposed T-Mobile-Sprint merger.
The two companies announced last month they had struck an all-stock deal to combine, arguing the $146 billion company would become a stronger competitor to former Bells Verizon and AT&T.
Critics counter that the deal will reduce choice in the burgeoning wireless broadband market.
The Senate Judiciary Committee's Antitrust Subcommittee will hold a hearing on the deal June 27, a committee spokesperson confirmed.
Some Senate Democrats, including Antitrust Subcommittee ranking member Amy Klobuchar (D-Minn.), have told the Department of Justice and the FCC that they have serious concerns about the proposed merger.
They did not say they opposed the deal, but they spelled out the reasons they thought it needed close scrutiny, including claims that combining the third and fourth largest wireless carriers is pro-competitive.