"Congressman, I was and I am 100 per cent sure this deal will be judged by the FCC and DOJ on the merits," Legere responded, referring to the two agencies reviewing the proposed merger, the Federal Communications Commission and the Department of Justice.
The two men talked over one another briefly, before Johnson interjected: "It doesn't pass the smell test with the American public. It looks like you're trying to purchase influence."
The flare-up comes weeks after The Washington Post uncovered detailed guest logs from the Trump hotel showing that top T-Mobile executives booked dozens of stays. Following the Post's report, lawmakers such as Rep. Pramila Jayapal, D-Wash., sent letters to T-Mobile inquiring about the stays.
On Tuesday, Jayapal said the issue of the hotel stays was significant because of allegations that President Trump may have interfered in the antitrust review of another deal, AT&T's purchase of Time Warner.
"There is reason to look at these questions of what happened at the Trump hotel, because it has been clear from quite a bit of reporting that President Trump appears to have involved himself in the AT&T/Time Warner merger and we want to make sure that is not happening today," she said.
Legere insisted that the choice to stay at the hotel was his alone and that it reflects his consistent practices in prior years.
"Except in 2015, you said you were never going to stay there," said Jayapal, referring to an old Twitter feud with Trump in which Legere had criticised his experience at a different Trump hotel.
It is unclear whether Legere committed never to stay at another Trump hotel - though he did not appear to dispute Jayapal's characterisation Tuesday afternoon - but in 2015 he did vow to leave one over a noise complaint.
"I am so happy to wake up in a hotel where every single item isn't labeled 'Trump,'" Legere tweeted after leaving the hotel, according to news reports at the time.
Rep. Val Demings, D-Fla., said she felt that where Legere chose to stay in Washington was not relevant, but that the "appearance of compromise or undue influence is."
Republican members needled Legere's Democratic critics, accusing them of pursuing a non-substantive line of questioning.
"I have said I would never stay in a La Quinta again, and I have stayed at a La Quinta subsequently," joked Florida Republican Matt Gaetz.
Not every moment of the hearing was devoted to Legere's hotel stays. Gaetz peppered Legere on a key issue facing the telecom industry: Huawei.
US officials have been trying to dissuade allies from using the Chinese technology giant's equipment in their networks over possible spying concerns, and T-Mobile on Tuesday said it did not use the company's gear.
T-Mobile's smartphone testing technology is at the center of federal charges of fraud and theft of trade secrets stemming from the alleged theft by Huawei employees of a robotic arm that T-Mobile used to test cell phones and then engineered a cover-up of the theft. The two units of Huawei named in the case have pleaded not guilty.
Lawmakers on both sides of the aisle raised concerns about what a merger between T-Mobile and Sprint would mean for consumer prices, employees' wages and innovation.
The two companies have promised that cellphone plan prices will not increase following the merger, and T-Mobile has vowed not to raise prices for at least three years after the deal closes.
It also has argued more generally that consumers will receive a better value for its service, which will benefit from enhanced capacity as a result of combining Sprint and T-Mobile's networks.
T-Mobile and Sprint have framed their merger as a vital step toward building a competitive, next-generation 5G network. A global race is currently on to launch the first mass-market 5G network that proponents promise will lead to the mainstreaming of new applications such as self-driving cars. T-Mobile and Sprint have said they expect to invest US$40b in 5G technology, should the merger be approved.
Some opponents insist that the deal will result in higher prices. Gigi Sohn, a consumer advocate and former FCC official, said T-Mobile's arguments about capacity were largely a distraction.
"Carnegie owned all the railroads," she told the lawmakers. "He owned all the capacity, but he was still a monopolist. Capacity is meaningless when it comes to setting prices."
