Executives for T-Mobile U.S. Inc. and Sprint Corp. will confront more questioning from lawmakers over their $26 billion merger as opponents of the deal continue to urge regulators to block it.

T-Mobile’s CEO John Legere and Sprint’s executive chairman Marcelo Claure face the Democratic-controlled House subcommittee on antitrust March 12, which is now led by David Cicilline (D-R.I), a critic of the deal.

The March 12 hearing marks the third time Legere and Claure will have to defend their merger...