The retail trading industry got a jolt earlier this week when Securities and Exchange Commission chairman Gary Gensler said that a ban on the contentious payments that brokerages such as Robinhood rely on to subsidize free trading was "on the table."

Those dollars, called payments for order flow, are a vital artery in the infrastructure that handles most retail traders' orders for stocks and options. Industrywide, these payments could reach record levels of $2bn this year for stock trades, and $4bn for options trades, according to Bloomberg Business Intelligence. The payments are Robinhood's main revenue source and help pay for its zero-commission approach that other retail brokers have followed.