The SEC has proposed rescinding Regulation NMS's trade-through rule and its companion prohibition on locked and crossed markets, two provisions that have shaped US equity order routing for nearly two decades.

The proposal, reported by JDSupra, targets the core of Rule 611 — the provision that forces protected quotations across venues and effectively outlaws locked or crossed markets in NMS stocks. If adopted, the change would touch how every buy-side and sell-side desk routes, slices and prices orders.

For routing desks, the stakes are concrete. The trade-through rule obliges brokers to execute at the best displayed price across protected venues or justify an exception. Removing it shifts the burden: desks would decide directly whether a slightly worse fill at a preferred venue beats a routed fill elsewhere, and smart order routers would need reprogramming to weigh that trade-off rather than comply with a mandate.

What does the rescission actually change?

Two mechanisms are in play:

• The trade-through rule, which bars executing at inferior prices when a protected quote exists on another venue.
• The locked/crossed market prohibition, which requires venues to avoid displaying quotes that lock or cross another venue's protected quote — the provision behind the quote-flickering and routing workarounds many desks already know.

Rescinding the lock prohibition would, in principle, permit standing locked or crossed markets — a state the current rule structure spends considerable plumbing to prevent. Whether that produces genuine price improvement or simply new arbitration between venues is untested in the modern US equity market.

Mandate or proposal?

Only a proposal. Nothing changes until the Commission adopts a final rule, sets an effective date and, where relevant, compliance deadlines. The JDSupra report gives none of those dates, and desks should treat every consequence discussed here as contingent until the release text specifies them.

What the report also does not say matters. It does not quantify expected changes in spreads, fill rates or routing costs. It does not state how the SEC would handle order-protection for options-linked or retail-sized flow, and it does not describe transitional periods for router vendors. Each gap is a question the comment file should answer.

Exchange and vendor statements ahead will deserve scrutiny rather than acceptance. Incumbent venues built queue-priority and lock-avoidance technology around Rule 611; their assessments of rescission costs carry obvious interest. Broker-dealer routing statistics, once published in response to the proposal, will show how much flow actually depends on trade-through protection today.

What desks should watch next

• The proposing release text, for the effective date and any compliance schedule.
• Comment letters from the major routing brokers and exchange operators, for workflow specifics.
• Router vendors' statements on configuration changes, which will set the real implementation timeline regardless of the rule's date.

The proposal is a structural question, not a trading signal; the practical test will come in the comment period, where the Commission must show that removing two decades of mandated protection improves execution rather than merely simplifying the rulebook.

By James Calloway