Former Federal Antitrust Enforcers Launch Plaintiff-Side Law Firm Simonsen Sussman LLP
June 17, 2025 (New York, NY) - Today four former senior federal enforcers launched a law firm dedicated to representing plaintiffs in high-impact antitrust and unfair competition litigation combatting the worst abuses of corporate power in our economy. Simonsen Sussman LLP seeks to fill significant gaps in enforcement with a clear mission: to help entrepreneurs, new entrants, small businesses, workers, and other victims of anticompetitive and unfair practices, as well as state and local governments, chart creative, strategic, and cost-effective paths to relief from violations of the competition laws.
The firm’s founders, Catherine Simonsen, Shaoul Sussman, Nicolas Stebinger, and Kate Brubacher, bring together decades of experience enforcing federal and state antitrust and unfair competition laws through government investigations and in private and public litigation across the country. Simonsen, Sussman, and Stebinger most recently served in Assistant Regional Director, Front Office, and Senior Trial Counsel roles in the Federal Trade Commission’s Bureau of Competition, while Brubacher co-founds the firm following her service as the United States Attorney for the District of Kansas.
“Antitrust law is at a significant inflection point,” said Simonsen. “Courts, enforcers, and practitioners increasingly recognize that large corporate interests have gone too far in watering down our statutes, stifling competition, and harming small businesses.”
“At the same time,” Brubacher added, “government enforcers are constrained and take a necessarily limited approach. And many private plaintiff firms are often singularly focused on damages, as opposed to stopping harmful market practices in time, while being subject to the excessive expert costs that traditional theories of liability require. We plan to help fill those gaps in this moment of great opportunity.”
The firm is well positioned to do so. The founders have deep experience developing not only traditional antitrust causes of action but also claims under historically neglected - yet powerful - competition laws. These include the Robinson-Patman Act, passed in the 1930s to protect small grocery stores from the abusive practices of large chain stores, and California’s Unfair Competition Law, a statute of sweeping coverage enacted for the purpose of preserving fair business competition.
“We see conduct through a different, more creative, and elegant lens. For example, where a traditional approach would only identify a monopolization claim requiring millions of dollars in lawyer and expert fees and a six-year case schedule, we see a more straightforward case under the price discrimination or unfair competition laws that can stop the conduct before it causes irreversible damage. Our guiding philosophy is to use every single tool in the toolkit to stop anticompetitive behavior on behalf of our clients,” said Sussman.
Stebinger added, “Through aggressive, targeted investigation, we intend to bring suits closer-in-time to when harm has occurred. We are nimble enough to take cases that would be infeasible for government enforcers. And because we will not face the same institutional constraints, we can forcefully make the most persuasive arguments on behalf of each and every client.”
Sussman is the managing partner of the firm’s founding and principal office in New York. The firm also has offices in Los Angles and Washington, DC, where Simonsen and Stebinger, respectively, serve as managing partners. The firm will have a fourth office in the Midwest where Brubacher is based.
For more information about Simonsen Sussman LLP or to inquire about potential representation, visit www.simonsensussman.com or contact the firm at inquiries@simonsensussman.com.