“No, that is not true,” Mr. Sutton replied.
Representative Joe Neguse, a Colorado Democrat, focused on Facebook.
He pointed out that not only is Facebook the world’s largest social network, but that those ranked third, fourth and sixth — WhatsApp, Facebook Messenger and Instagram — are Facebook properties.
Owning the four of the top six players in a market, Mr. Neguse said, spoke for itself. “We have a word for that,” he said. “It is called monopoly.”
Earlier in the day, in the hearing about Facebook’s cryptocurrency project, Libra, lawmakers grilled David Marcus, a top executive.
The company has a bold goal with the project: to offer an alternative financial system that makes it possible to send money around the world with few fees. But the company has run into bipartisan resistance from Washington, including the White House.
The initiative is far from the first effort of its kind. The best-known cryptocurrency, Bitcoin, is in wide circulation, and it introduced the idea of digital currencies that are free from government control.
But the Libra effort has put a spotlight on cryptocurrencies and amplified the voices of critics who say the technology has little value beyond speculative investing and illegal transactions, like online drug sales. Last week, the chair of the Federal Reserve, Jerome H. Powell, said Libra raised “serious concerns” around “money laundering, consumer protection and financial stability.” Mr. Trump and the treasury secretary, Steven Mnuchin, have also criticized Libra and other cryptocurrencies in the past week.