Rule 5310 has stood in roughly its current, principles-based form since 1968 — outlasting the birth of Regulation NMS, the rise of algorithmic trading, and every market structure shift since. On July 24, 2026, FINRA published Regulatory Notice 26-15, requesting comment on how it should modernize the interpretive guidance sitting on top of that rule. It isn't proposing to rewrite Rule 5310 itself, and it isn't required reading yet — but the reason it's on the table now is worth every broker-dealer's attention.
The trigger is the SEC's own proposal to rescind Rule 611 of Regulation NMS, the "trade-through" rule that has barred trading centers from executing at a price worse than the best displayed quote elsewhere for more than twenty years. The SEC has said all along that Rule 611 "in no way lessens a broker-dealer's duty of best execution" — it's a structural floor, not a substitute for the reasonable-diligence standard under Rule 5310. But if that floor disappears, FINRA wants member firms to weigh in on what happens to the practices that were built around it.
Why this matters even though nothing has changed yet
Comments are due September 25, 2026, and FINRA has been explicit that it believes Rule 5310's principles-based text remains "appropriately calibrated." What's actually in play is the twenty-plus years of interpretive guidance layered on top of it — guidance many firms have built order-routing logic, execution-quality reviews, and smart order routers around. If Rule 611 goes away, some of that guidance may need to catch up.
- The NBBO's role as a benchmark. Without protected quotations, is the National Best Bid and Offer still the right yardstick for price improvement — or do firms need alternative benchmarks for measuring execution quality?
- Venue connection decisions. Firms currently connect to venues in part to satisfy Rule 611. FINRA is asking what should govern those decisions once that requirement is gone — volume, access fees, latency, something else.
- Order-by-order vs. regular-and-rigorous review. FINRA is asking whether smart order routers with built-in best-execution logic could satisfy an order-by-order review standard, and whether that standard still makes sense for internalized flow.
- Access fees and transaction costs. With the SEC separately reviewing access fee caps under Rule 610(c), FINRA wants input on how fees should factor into routing decisions and whether better-priced-but-higher-cost venues should be weighed differently.
- Retail vs. institutional expectations. FINRA is asking whether best execution guidance should more explicitly distinguish what institutional customers value (information leakage, execution certainty on size) from retail expectations (price, speed).
How Compliers Can Help
Best execution reviews are a core piece of the supervisory testing we build for clients — whether that's the quarterly "regular and rigorous" review process itself or preparing a comment letter if your firm wants a voice in this rulemaking. See our AML, 3120 & Branch Audits page for how we support ongoing supervisory testing programs like this one.
What to do between now and September 25
This is a request for comment, not a rule proposal — there's no compliance deadline attached to it yet. But firms whose order-routing and execution-quality review processes lean on Rule 611 as an implicit backstop should start thinking now about how those processes would hold up without it. Firms with a real stake in the outcome — particularly those running significant retail or institutional order flow — also have a genuine opportunity to shape what FINRA's next round of guidance actually says, rather than reacting to it after the fact.