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Lowenstein Sandler LLP

Jack Sidorov

Jack Sidorov

Senior Counsel


  • Litigation
  • Antitrust & Trade Regulation
  • White Collar Criminal Defense

WSG Practice Industries



Jack brings 36 years of experience at the U.S. Department of Justice (DOJ) Antitrust Division to his practice, which focuses on advising on antitrust issues and premerger notification requirements. He is a noted authority on premerger notification law, and his 2014 addition to the firm "bolster[ed] Lowenstein's ability to provide M&A counsel to private equity, hedge fund, and venture capital clients" (Law360).

Prior to joining the Washington, D.C. office of the firm, Jack served as the DOJ's primary expert on premerger notification law, procedures, and policies under the Hart-Scott-Rodino (HSR) Act, providing HSR-related advice to the Assistant Attorney General for Antitrust and throughout the Antitrust Division. He worked closely with the Federal Trade Commission's (FTC's) Premerger Notification Office on numerous HSR rulemakings, including rules promulgating HSR exemptions (1996), implementing legislative changes to the HSR Act (2002), revising the HSR treatment of partnerships and limited liability companies (2005), and making substantial changes to the HSR Form designed to improve the utility of the form to the FTC and DOJ while reducing burden on filing parties (2011).

Jack played a leading role in roughly 50 civil penalty compliance cases brought under the HSR Act, working to develop and articulate the legal theories underlying these cases, up to and including the DOJ's November 2014 case alleging and settling gun-jumping claims against Flakeboard and SierraPine. The settlement required the companies to pay a combined $3.8 million in civil penalties for violating the HSR Act and further required Flakeboard to disgorge an additional $1.15 million in illegally obtained profits for violating Section 1 of the Sherman Antitrust Act.

Working with the Antitrust Division's Foreign Commerce Section, Jack regularly counseled other countries on premerger notification law and best practices through various international antitrust bodies, including the International Competition Network, which he continues to participate in, and the OECD Competition Committee.

While at the DOJ, Jack also advised on a range of non-HSR issues, from monopolization law relating to loyalty discounts and other unilateral conduct to antitrust issues arising in the context of college and professional sports. Early in his career, Jack was part of the DOJ's AT&T Relief Task Force, developing plans for the relief ultimately obtained in the monopolization case against AT&T and preparing the relief case for trial.

Before embarking on his legal career, Jack founded and served as Commissioner of the World Stickball Association, which played its games on the campus of Harvard Law School. His walk-off home run, which propelled the Long Island Sound to victory over the Prague Noses in Stickbowl III, was featured on NBC.

Bar Admissions

    District of Columbia


Harvard Law School (J.D. 1976), magna cum laude
Johns Hopkins University (B.A. 1973), Quantitative Studies with concentration in Economics, General Honors, Phi Beta Kappa
Areas of Practice

Antitrust & Trade Regulation | Litigation | White Collar Criminal Defense


Antitrust Does Not Shelter in Place During a Pandemic, Part 2: Don’t Claim the Failing Firm Defense Unless You’re Really Failing
Lowenstein Sandler LLP, May 2020

The Federal Trade Commission (FTC) has reminded us that the “failing firm defense” is much harder to pull off than might be imagined, and that the antitrust agencies will closely analyze all “failing company” claims even during the coronavirus pandemic. In its May 27 blog post, "On “Failing” Firms — and Miraculous Recoveries,"the FTC emphasized that the defense is difficult to make and, even more to the point, often not true...

The Certainty of Antitrust Review in Uncertain Times
Lowenstein Sandler LLP, April 2020

The Federal Trade Commission (FTC) Bureau of Competition issued a reminder yesterday, April 6, that it “must continue to analyze carefully the potential effects of proposed transactions and business conduct” and that it “will not suspend our usual rigorous approach to ferreting out anticompetitive harm and seeking relief, even in the face of uncertainty...

U.S. and European Antitrust Authorities Provide Updated Guidance on Joint Activity During COVID-19
Lowenstein Sandler LLP, March 2020

On March 24, the U.S. Department of Justice Antitrust Division (the Antitrust Division) and the Federal Trade Commission (FTC) (collectively, the Agencies) issued a joint statement detailing a new expedited process for review of proposed collaborations aimed at protecting the health and safety of Americans during the COVID-19 pandemic, to ensure that such collaborations comply with federal antitrust law...

Additional Articles

On Sept. 26, the U.S. Department of Justice filed a lawsuit challenging Parker Hannifin Corporation’s consummated acquisition of Clarcor Inc., a transaction that was reported to the DOJ and the Federal Trade Commission under the Hart-ScottRodino Act and for which the HSR waiting period had expired.

The complaint alleges that the merger substantially lessened competition and created a monopoly in markets for aviation fuel filtration products in the United States, and seeks divestiture of either Parker’s or Clarcor’s aviation fuel filtration assets.

The Hart-Scott-Rodino Act requires pre-acquisition notification to the Federal Trade Commission and U.S. Department of Justice of certain acquisitions of voting securities, assets and noncorporate (e.g., LLC) interests so as to enable the agencies to conduct pre-acquisition antitrust review. Acquisitions of minority interests of voting securities (“partial acquisitions”) may trigger HSR, and the rules that have been in effect since the inception of the HSR program in 1978 are complex and can require parties to make multiple HSR filings over time and at different ownership levels even if a 50 percent or greater interest is never reached.

With a working group within the International Competition Network having recently advised that “[a]cquisitions of a minority interest should not be included in the scope of merger review if they are unlikely to be competitively significant”[1] and with an administration focused on deregulation, this is a good time to revisit the HSR treatment of partial acquisitions in order to see whether HSR coverage can be narrowed without sacrificing the usefulness of HSR as an antitrust enforcement tool.

This article comes in two parts. Part one outlines HSR treatment of partial acquisitions and suggests three major changes. Part two describes the rationale for and implementation of those changes.

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