The SEC Wants to Repeal the Rule That Forces a Trade to the Best Displayed Price

When a U.S. stock trades, Rule 611 of Regulation NMS says the venue executing it may not print a price worse than the best bid or offer displayed on another exchange. That obligation, adopted in 2005 and known as the order protection or trade-through rule, is one of the load-bearing walls of American equity market structure. The Securities and Exchange Commission has proposed taking it out.

What the two rules do now

Rule 611 requires trading centers to maintain policies reasonably designed to prevent trade-throughs of protected quotations - the top-of-book quotes displayed by exchanges and FINRA's Alternative Display Facility. It applies during regular trading hours and carries nine exceptions, among them intermarket sweep orders and a one-second window covering quotes that move faster than a router can react.

Rule 610(e) is the companion. It requires exchanges and FINRA to have rules obliging members to reasonably avoid displaying quotations that lock or cross a protected quotation. A market is locked when the best bid equals the best offer, and crossed when the best bid is above the best offer.

The Commission's argument

• The linkages that were missing in 2005 now exist: markets are automated, interconnected and fast, and sophisticated routing technology is widely available
• Best execution obligations continue to apply to broker-dealers whether or not Rule 611 is on the books
• Rule 611 has contributed to a proliferation of complex order types, venue fragmentation and compliance cost
• By guaranteeing that a displayed quote receives routed order flow, the rule underwrites market data and connectivity revenue for exchanges that might not otherwise attract volume
• Rescinding Rule 610(e) could permit locked markets, which the Commission suggests may reflect greater price transparency and allow tighter spreads

The numbers the SEC leans on

Seventeen exchanges trade NMS stocks in 2026, against eight in 2005. Non-displayed trading has increased substantially and, since the end of 2024, regularly exceeds 50% of overall volume. The Commission's reading is that top-of-book displayed size at any single venue is small, so an institution working a large order faces fragmentation costs that the protected-quote regime helps entrench.

What critics point to

The opposing case, set out in practitioner analysis of the proposal, runs the other way on each point. Trades could lawfully execute at prices that are currently prohibited as trade-throughs. Locked and crossed quotations could appear in the displayed market, making the tape harder to read. Exchanges would have less incentive to display competitively priced quotes if displaying one no longer guarantees order flow, and smaller venues could lose the economics that keep them connected. Broker-dealers would carry more of the burden through best execution analysis, and would need to document why a given trade-through price was justified.

Why it matters

For most people the trade-through rule is invisible: it operates between the moment an order leaves a broker and the moment it prints. But it is the reason the displayed national best bid and offer functions as a binding reference rather than an advisory one. Removing it would move that protection from a rule enforced at the venue to a duty enforced at the broker. This article explains a pending rulemaking and is not advice about trading or any security.