Introduction
Regulation M is the SEC's anti-manipulation framework governing trading activity during a securities offering. Adopted in 1996 and amended periodically since, the rules restrict distribution participants (underwriters and other broker-dealers in the syndicate), issuers, and selling shareholders from bidding for or purchasing the offered security during a defined "restricted period" before the offering prices. The framework is designed to prevent the parties with economic interest in a high cleared price from artificially supporting the stock during the distribution. Every ECM banker must understand Reg M because the rules govern what the bank's trading desk, the issuer, and any selling shareholder can and cannot do during a live deal, and the consequences of violation are severe (SEC enforcement, fines, and reputational damage).
The Restricted Period Framework
The restricted period is the time window during which Reg M prohibitions apply to distribution participants and issuers.
One-Day Versus Five-Day Restricted Period
The applicable period depends on the security's average daily trading volume (ADTV) and the issuer's public float. Securities with at least $100,000 of ADTV from an issuer with at least $25 million of public float have a one-day restricted period (commencing one business day before pricing). Securities falling below either threshold have a five-day restricted period. Most US listed equities meet both thresholds and operate under the one-day window.
- Restricted Period
The defined window during which Regulation M prohibitions on bidding for and purchasing the offered security apply to distribution participants, issuers, and selling shareholders. One business day before pricing for actively-traded securities (ADTV of at least $100,000 and public float of at least $25 million); five business days before pricing for less-liquid securities. Most US listed equities operate under the one-day window.
What the Restricted Period Restricts
During the restricted period, distribution participants (Rule 101), issuers (Rule 102), and selling shareholders (Rule 102) cannot bid for or purchase the covered security or attempt to induce others to do so, subject to the carve-outs discussed below. The restriction extends to the parties' affiliated purchasers, which is why bank trading desks must coordinate with the syndicate desk to ensure the bank's broader trading activity does not inadvertently breach Rule 101 during a live deal.
| Rule | Who | What it does |
|---|---|---|
| 100 | Definitions | Defines covered terms (covered security, distribution participant, restricted period) |
| 101 | Distribution participants | Restricts bank/syndicate bidding and purchasing during restricted period |
| 102 | Issuers and selling SHs | Parallel restriction on issuer and selling shareholders |
| 103 | Passive market making | Carve-out letting Nasdaq market makers continue liquidity-provision under conditions |
| 104 | Stabilization | Carve-out permitting underwriter stabilizing transactions and greenshoe support |
| 105 | Short sellers | Prohibits covering pre-pricing shorts with offering shares |
Rules 101 and 102: Distribution Participants and Issuers
Rule 101 governs underwriters, syndicate members, and other broker-dealers participating in the shelf takedown, prohibiting the bank from purchasing the security in its own account during the restricted period (subject to carve-outs). Rule 102 applies the parallel restriction to issuers and selling shareholders: the issuer cannot repurchase its stock during the period (active buybacks are suspended or covered by 10b5-1 plans) and selling shareholders cannot purchase additional offered shares.
Rules 103 and 104: Passive Market Making and Stabilization
Rule 103 lets broker-dealers acting as registered market makers in Nasdaq securities continue making markets during the restricted period under specific conditions (cannot bid above the highest independent bid, must comply with capacity and notification limits). The carve-out preserves orderly liquidity-provision in the stock during the distribution. Rule 104 permits underwriter stabilization (bids placed to peg, fix, or maintain price) under disclosure and reporting conditions; stabilization is the mechanism behind the IPO greenshoe where the syndicate's short from the over-allotment is covered through stabilizing purchases.
Rule 105: Short Selling Restriction
Rule 105 prohibits short sellers from covering pre-pricing short positions with offering shares purchased from a syndicate broker, when the short was established within the five business days before pricing. The rule prevents the manipulative pattern where a seller drives the stock down to widen the offering's discount and then covers cheap. Rule 105 violations are routinely detected through trade-data analysis and rank as one of the SEC's most-pursued enforcement areas in equity offerings.
A one-day restricted period, carve-outs for passive market-making and stabilization, and Rule 105's short-cover ban: that is the trading-rule plumbing every US follow-on operates inside. With the regulatory layer mapped end to end, the section closes by turning the entire toolkit (marketed, bought deal, block, ATM, rights, ASR, secondary) into a single decision framework. Choosing the right follow-on product is the final article.
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