Wall Street’s top regulator is calling for a broad review of rules that underpin U.S. equity trading, the latest evidence that the meme-stock mayhem is likely to trigger an overhaul.

U.S. Securities and Exchange Commission Chair Gary Gensler said Wednesday that he’s asked the agency’s staff to examine best execution requirements -- legal mandates that ostensibly force brokers to process customers’ orders at advantageous prices. Gensler added that the process for settling transactions could be shortened to the same day. He also reiterated concerns that companies behind popular smartphone apps have profit incentives to hook consumers on trading.

Trading rules have come under scrutiny amid wild swings for GameStop Corp., AMC Entertainment Holdings Inc. and other companies. While Gensler didn’t mention them by name, he directed some of his most pointed comments to market makers like Citadel Securities LLC and Virtu Financial Inc. Those firms pay retail brokers a fee to execute clients’ trade orders.

“Brokers profit when investors trade,” Gensler said in a speech at the Piper Sandler Global Exchange & FinTech Conference. “For those brokers who have these arrangements -- and not all do -- higher trading volume generates more payment for order flow. What makes the current zero-commission brokerage environment different is that investors do not see their costs as they’re executing trades, so they may perceive them as free.”

Virtu slid 7.7 per cent in New York trading, its biggest one-day slump since September. Interactive Brokers Group Inc. and Charles Schwab Corp. also declined.

Gensler, who took over the agency in April, has said previously that there are inherent conflicts tied to payment for order flow and that the SEC was looking closely at whether it needs to revamp regulations.

On Wednesday, Gensler said that he’d directed the SEC staff to focus on whether retail investors are indeed getting the best deal for their trades. He raised issues around best-execution requirements that brokers must comply with when handling trades.

Gensler also questioned whether a national price reference known as the NBBO, which is used to determine whether brokers are meeting their best execution requirements, was an accurate benchmark for the market. He said that it might not be because a significant portion of trading is executed by wholesale brokerages and not on traditional platforms like the New York Stock Exchange.

During an interview on CNBC following the event, Gensler went further. He questioned the brokerage industry’s argument that payment-for-order-flow arrangements have allowed retail investors to trade stocks for free.

“I think that’s a mis-perception -- it’s not free trading,” Gensler said. “It is zero commission, but not necessarily free,” he added, noting that the data brokerages gain is valuable.

In his speech, Gensler noted that “gamification” features common in apps encourage investors to trade more. He added that the uptick in trading results in “more payment for order flow for brokers.” Critics have most closely associated gamification with Robinhood Markets, though Gensler didn’t mention the firm by name.

“We lool forward to engaging with the SEC through its formal rulemaking process as it considers changes to the current market structure, which is working so well for an increasingly diverse universe of investors,” Robinhood said in a statement.