When the heroes of Michael Lewis’ book Flash Boys launched the IEX exchange in 2016, Wall Street was split on the benefits of its attempt to slow high-speed traders by a fraction of a second. This June, after Cboe Global Markets proposed a speed bump for one of its stock exchanges, most of Wall Street said they hated the idea.

Mutual fund managers and institutional brokers who cheered IEX are now asking the US Securities and Exchange Commission to block Cboe’s plan. As the SEC deliberates, Wall Street opponents of the plan outnumber supporters six-to-one on the agency’s comment web page. Among the critics: the mutual fund industry’s Investment Company Institute, the Chamber of Commerce, several hedge fund trade groups, and an influential market commentator named R.T. Leuchtkafer.