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William Mack

William B. Mack is a co-chair of the Financial Regulatory & Compliance Practice. He is experienced in advising companies on regulatory and compliance matters relating to the Securities and Exchange Commission regulations, the Exchange Act, Anti-Money Laundering laws and Financial Industry Regulatory Authority (FINRA) rules.

William’s practice involves all aspects of broker-dealer regulation, including Self-Regulatory Organization (SRO) membership, supervision, employment, research, soft dollar arrangements, chaperoning of foreign broker-dealers, social media, use of foreign finders, anti-money laundering rules, alternative trading systems (ATS), exchanges, and market making issues. He also provides regulatory guidance to investment banking clients in connection with securities offerings and related trading issues.

William advises firms in the FINRA new membership (NMA) and the continuing membership (CMA) processes. William assists firms to develop or amend their written supervisory procedures and compliance manuals.

William routinely represents clients who are negotiating placement agent agreements, foreign finders agreements, clearing agreements, agreements with registered representatives and expense-sharing agreements.

William assists broker-dealers and their associated persons to respond to regulatory examinations and inquiries and provides effective representation in a range of enforcement proceedings with the SEC, FINRA, NYSE, state and foreign regulatory authorities. He regularly prepares and defends witnesses in FINRA on-the-record interviews and SEC testimony. Enforcement matters have involved issues including market manipulation, supervision, customer defalcations, insider trading, anti-money laundering, distribution of unregistered securities, direct market access, market making, soft dollar arrangements, cross border trading, electronic intrusion and customer impersonation, sales practices, supervision, private placements, ETFs, indexes, and other securities products.

William regularly addresses questions with respect to what activities require or are exempt from broker-dealer registration. William assists firms in obtaining guidance, interpretive letters, and no-action relief from FINRA and the SEC with respect to novel securities issues and the creation of new products and services. William also advises clients on cryptocurrency, tokenization, NFTs, DeFi structures, and digital asset exchanges and trading.

Prior to joining the firm, William was a Principal Counsel for Enforcement at FINRA. Before FINRA, he was the Director of the Executive Secretariat in the Office of the U.S. Trade Representative. William also served as a Deputy Associate Counsel at the White House, advising primarily on appointments and investigations. Before the White House, he practiced at large firms in New York. William clerked for Judge Robert L. Carter in the Southern District of New York.

On Sept. 18, 2023, the New York State Department of Financial Services (NYDFS) issued a press release announcing updates to its ongoing oversight of the digital asset space, including (1)…

Continue Reading NYDFS Updates Guidance on Virtual Coin-Listing/Delisting Frameworks and the Greenlist

On Aug. 29, 2023, the U.S. Court of Appeals for the District of Columbia Circuit (Court) vacated the U.S. Securities and Exchange Commission (Commission)’s denial of Grayscale Investments, LLC (Grayscale)’s…

Continue Reading SEC Denial of Proposed Bitcoin Exchange-Traded Product Arbitrary and Capricious: DC Circuit

On Aug. 28, 2023, the Securities and Exchange Commission (Commission) charged Impact Theory, LLC, a media and entertainment company, with violating Sections 5(a) and 5(c) of the Securities Act of…

Continue Reading SEC Charges Media and Entertainment Co. for Unregistered Offering of NFTs

On May 17, 2023, Prometheum Ember Capital LLC (Prometheum Ember Capital), a subsidiary of Prometheum Inc., received approval from the Financial Industry Regulatory Authority (FINRA) to…

Continue Reading FINRA Approves Prometheum Ember Capital LLC to Operate as Special Purpose Broker-Dealer for Digital Assets

On Dec. 14, 2022, the SEC announced charges against eight social media influencers in a $100 million securities fraud scheme in which they allegedly used social media platforms to tout…

Continue Reading 8 Influencers Charged in $100 Million Securities Fraud Scheme

On Nov. 7, 2022, the U.S. District Court for the District of New Hampshire granted the Securities and Exchange Commission’s motion for summary judgment in SEC v. LBRY, Inc.…

Continue Reading SEC v. LBRY, Inc.: The SEC’s Latest Crypto Victory


On Dec. 12, 2020, the U.S. Securities and Exchange Commission brought what crypto followers consider one of the most consequential enforcement actions related to the sale of cryptocurrency since the…

Continue Reading Crypto Showdown: SEC’s Lawsuit Against Ripple Labs Reaches Critical Juncture