Lawmakers said in a House hearing on Wednesday that Facebook’s plan to enter the world of cryptocurrency and global finance could threaten sovereign currencies or even destabilize governments.

A day after a similarly critical Senate hearing, it was the House Financial Services Committee’s turn. David Marcus, a Facebook executive, faced over four hours of questions about Facebook’s plans for a cryptocurrency called Libra. As was the case on Tuesday, Mr. Marcus was dogged by his company’s controversial reputation as well as skepticism of the legal uses of cryptocurrencies.

“This is the biggest thing this committee will deal with this decade,” said Representative Brad Sherman, a Democrat from California. “This is a godsend to drug dealers and tax evaders.”

When Facebook announced Libra in June, it said it wanted to create a new global financial system. The initiative, if successful, could put digital wallets in the hands of the more than two billion people who use Messenger and WhatsApp, the messaging platforms owned by Facebook.