Members of Congress are fed up with the state of cellphone coverage in the United States, and on Wednesday, they weren’t afraid to lodge their complaints personally — with the leaders of some of the country’s biggest wireless networks.

As Sprint and T-Mobile went to Capitol Hill to defend their $26 billion proposed merger, lawmakers buttonholed T-Mobile’s chief executive, John Legere, and Sprint’s executive chairman, Marcelo Claure, on the frustrating inability to get a cell signal in many parts of the country, particularly in rural areas.

Waving a coverage map of his state in the middle of a congressional hearing, Rep. Peter Welch (D-Vt.) said that despite flashy promises to build a dazzling 5G network, wireless carriers can scarcely manage to serve Vermont with regular 4G LTE.

“In a lot of Vermont, we have no-G,” said Welch. “These maps are bogus.”

When Claure tried to shift the blame to AT&T and Verizon, saying Sprint’s network often relies on those companies’ infrastructure in many areas, Welch interrupted.

“These are no good! These are phony maps!” he bellowed.

Welch wasn’t alone in taking the carriers to task. Rep. Tom O’Halleran (D-Ariz.) complained that when he returns home to his district, “Half the time that map says I should be covered. Half the time I’m not, by anybody.”

And minutes earlier, Rep. Ben Ray Luján (D) quipped that he often gets better Internet service on airplanes as he’s flying over his home state of New Mexico than he does while on the ground there.

“I don’t understand that,” he said.

The lawmakers’ pique follows a study last year in which a Vermont Department of Public Service employee crisscrossed the state in a car outfitted with mobile networking equipment to test the strength of each carrier’s service — and their marketing. The car couldn’t reach every part of the state because of its mountainous terrain, but even in more-accessible areas, the study found that actual service frequently failed to live up to the coverage maps.

T-Mobile and Sprint vowed that if their merger is approved by regulators, coverage in rural areas will improve as the combined company invests more in those areas.

But Carri Bennet, a witness at the hearing who is an attorney for rural carriers, said the bigger players “have had more than 20 years to build out to rural America” and questioned whether to reward the companies with the merger.

The accuracy of the country’s broadband maps has come under mounting scrutiny as more Americans come to view Internet access as an essential tool.

On Wednesday, the Commerce Department launched an initiative aimed at improving broadband mapping by drawing on more data than what the Federal Communications Commission gathers from Internet providers, with a goal of launching an interactive mapping tool by September.

Last year, the FCC announced it was looking into concerns that companies may have submitted inaccurate coverage maps as part of a bidding process for a federal infrastructure program.

“A preliminary review of speed test data submitted through the challenge process suggested significant violations of the Commission’s rules,” FCC Chairman Ajit Pai said in a statement at the time. “That’s why I’ve ordered an investigation into these matters. We must ensure that the data is accurate before we can proceed.”

Democratic FCC Commissioner Jessica Rosenworcel called the situation “a mess,” saying federal broadband maps must more accurately reflect the reality on the ground.

On Thursday, the FCC voted to approve a series of guidelines for what will ultimately be a 10-year funding process for rural broadband, with the agency planning to disburse nearly $1.5 billion in federal subsidies to wire up more than 700,000 homes and businesses in 45 states, according to officials.

When it comes to wired networks, the government considers an entire census block to be served by fixed broadband if an Internet provider offers download speeds of at least 25 megabits per second to one area household. Consumer advocates have said this approach risks overstating the number of U.S. households that are served by broadband, because many households without high-speed Internet may be located in these census blocks.

On Wednesday, Legere pitched the merger as a potential solution, saying that combining with Sprint would give T-Mobile the power not only to compete with AT&T and Verizon in mobile data, but also to challenge cable companies with a wireless network that offers comparable speeds to companies such as Comcast or Cox.

Whether that’s really true will be up to the Justice Department — and the FCC — to determine.