Investors and Wall Street trade groups are criticizing the SEC's proposal to eliminate the decades-old trade-through rule, which requires trading platforms to execute orders at the best available price across exchanges. Hundreds of public comments were filed before Monday's deadline warning the plan would harm the U.S. stock market.

The rule ensures that if General Motors shares trade at $80 on one exchange and $79.99 on another, orders must be routed to the cheaper venue. SEC Chairman Paul Atkins, a Trump appointee, argues scrapping the rule would "simplify market structure and reduce costs for market participants."

Atkins, who voted against the rule in 2005, claims it caused unintended consequences including a proliferation of exchanges. There are now 18 stock exchanges, most handling less than 1% of total U.S. trading volume, up from eight in 2005, according to SEC data.