WASHINGTON — Key players in the GameStop saga faced questions Thursday from House lawmakers concerned that even as investing becomes more democratized, the scales are still tilted in favor of the big Wall Street institutions.

GameStop shares soared 1,600% in January before retreating sharply. The drama entangled huge short-selling hedge funds, a social media message board and ordinary investors wanting in on the hottest new trade.

Some of the toughest questions and harshest criticism was directed at Vlad Tenev, CEO of Robinhood, which operates an online trading platform that is popular with individual investors. Tenev defended Robinhood against allegations that trading restrictions it put in place at the height of the GameStop frenzy disadvantaged those smaller investors in favor of bigger institutional clients.

The head of the Financial Services Committee, Rep. Maxine Waters, D-Calif., grilled Tenev on those restrictions. She also asked Tenev about Robinhood’s close relationship with Citadel Securities, which she maintains is a conflict of interest. At issue is the common practice in the securities markets of payment for order flow, in which Wall Street trading firms such as Citadel Securities pay companies like Robinhood to send them their customers’ orders for execution. In addition, platforms like Robinhood give the trading firms data on stocks its users are buying and selling.

Both Tenev and Ken Griffin, the CEO of Citadel, denied that Citadel had any role in Robinhood’s decision to restrict trading in volatile stocks.

Tenev said Robinhood imposed the trading restrictions solely to meet capital requirements.