Madelyn Petersen’s practice focuses on litigating class actions on behalf of consumers who have been misled, deceived or harmed by large corporations.
Prior to joining Cohen Milstein, Madelyn was a law fellow at the firm. In this role, she worked across practices and was involved in litigating individual and class action cases at the district and appellate levels. She was also a law clerk to the Honorable William Dimitrouleas of the United States District Court for the Southern District of Florida.
While at Harvard Law School, Madelyn was the managing editor of Harvard Journal of Law and Gender and online content editor for Harvard Civil Rights-Civil Liberties Law Review. While in law school, she was also a board member of the Harvard Prison Legal Assistance Project and participated in Harvard Law School’s International Human Rights Clinic. She was also a legal intern for the Corporate Accountability Lab, the Advancement Project, and Oxfam America.
- District of Columbia
- Harvard Law School, J.D., 2019
- University of Nebraska-Lincoln, B.A., 2016
Law Fellow, Cohen Milstein Sellers & Toll PLLC (2021 – 2022)
Law Clerk, Hon. William Dimitrouleas, U.S. District Court, Southern District of Florida (2019 -2021)
Current Cases
General Motors Litigation
General Motors Litigation (E.D. Mich.): Cohen Milstein, as court-appointed Lead Counsel and Plaintiff Steering Committee Chair, represents a certified class of consumers in more than 25 states who purchased or leased new and used vehicles manufactured by GM in a consolidated breach of warranty and deceptive and fraudulent business practices class action against GM. Plaintiffs bring their claims under state consumer protection statutes and express and implied warranty law of their respective states, related to GM's manufacture and sale of defective eight-speed automatic transmissions (GM 8L90 or the 8L45), manufactured by between 2015 and 2019.
DZ Reserve et al. v. Meta Platforms
DZ Reserve et al. v. Meta Platforms (N.D. Cal.): Cohen Milstein represents advertisers who claim that Facebook’s Potential Reach metric is false and misleading due to systemic inflation of the Potential Reach. The court granted class certification on March 29, 2022. On January 13, 2025, The U.S. Supreme Court declined Defendant’s petition to review the Ninth Circuit’s 2023 opinion affirming the lower court's 2022 class certification.
Belyea, et al. v. GreenSky, Inc., et al.
Belyea, et al. v. GreenSky, Inc., et al. (N.D. Cal.): Cohen Milstein, as Co-Lead Counsel, is reparenting consumers in this certified false advertising and unfair business practices class action, alleging that GreenSky, a financial technology company, operates in California as an unlicensed and unregistered credit services organization, finance lender, and broker in violation of California Financing Law the Credit Services Act of 1984, and other federal and state laws.
Siemens’ Arc Fault Circuit Interrupters (AFCI) Litigation
Kevin Brnich Electric LLC, et al. v. Siemens Industry, Inc. (N.D. Ga.): Cohen Milstein is Co-Lead Counsel in this false advertising and product defect consumer protection class action, alleging that Siemens’ AFCI circuit breakers are defective and Siemens misrepresents and omits information about the quality of its AFCIs.
Baus, et al. v. Ford Motor Company
Baus, et al. v. Ford Motor Company (E.D. Mich.): Cohen Milstein represents plaintiffs who purchased or leased vehicles manufactured by Ford Motor Company in a consolidated breach of warranty and deceptive and fraudulent business practices class action against Ford Motor Company. Plaintiffs bring their claims under the Magnuson Moss Warranty Act and the consumer fraud statutes of their respective states, related to Ford’s manufacture and sale of defective Ford F-150 pickup trucks, Model Years 2018-2020 equipped with 5.0L engines.
Past Cases
TR CLEAR Data Privacy Litigation
Brooks, et al. v. Thomson Reuters (N.D. Cal.): Cohen Milstein is representing a class of putative plaintiffs who claim that Thomson Reuters’s CLEAR platform not only surreptitiously collects vast quantities of Californians’ personal data but then sells this information to third parties, including commercial and government entities. On February 21, 2025, the court granted final approval of a $27.5 million settlement plus injunctive relief.
February 25, 2025
GreenSky Loan Class Action Certified in Calif. Court
A California federal judge has granted class certification to consumers suing GreenSky Inc. over alleged unlawful loan transaction fees, finding that expert analysis showed merchants likely passed these fees onto borrowers.
In the News | Law360
January 13, 2025
High Court Won’t Scrutinize Huge Class Of Meta Advertisers
The U.S. Supreme Court declined to assess the certification of an enormous class of businesses that social media colossus Meta Platforms allegedly defrauded by inflating the reach of Facebook and Instagram advertisements, upping the odds of a major payout in the closely watched case.
In the News | Law360
August 28, 2024
Sixth Circuit Affirms Class Certification in Massive Defective Transmission Lawsuit Against GM
Today, the U.S. Court of Appeals for the Sixth Circuit affirmed a class certification granted on March 20, 2023 in a massive class action lawsuit across 26 states against General Motors that alleges the car manufacturer violated state consumer protection statutes by knowingly putting cars with faulty transmissions on the road, endangering drivers, passengers, and pedestrians.
Press Releases | Cohen Milstein
August 8, 2024
9th Circ. Won’t Rethink OK’ing Ad Class Cert. Against Meta
The Ninth Circuit refused Thursday to rethink a split panel decision affirming certification of a damages class of potentially millions of advertisers who were allegedly deceived about Facebook’s “potential reach” tool, rejecting Meta Platforms Inc.’s warnings of unchecked fraud class actions. According to the one-page order, U.S. Circuit Judges J. Clifford Wallace and Sidney R. […]
In the News | Law360
April 17, 2024
Second Class Action Filed Against General Motors for Defective Transmissions
Purchasers of new and used GM vehicles manufactured between 2015 – 2019 equipped with GM’s 8-speed transmission filed a product defect and consumer protection class action against GM for an alleged defective transmission design of GM’s Hydra-Matic 8L90 transmission or Hydra-Matic 8L45 transmission, which causes vehicles to suddenly lurch forward, shudder, and experience significant delays in acceleration. The plaintiffs in ten states claim GM was aware of the transmission defects that pose safety risks to drivers and passengers.
Press Releases | Cohen Milstein
March 22, 2024
9th Circ. Partially Backs Meta Class Cert. In Ad Reach Row
A split Ninth Circuit panel on Thursday affirmed certification of a damages class of Meta Platforms advertisers who were allegedly deceived about Facebook’s “potential reach” tool, but upended certification of an injunction class, telling the district court to take a fresh look at whether the lead plaintiff actually has standing. The panel majority, in a […]
In the News | Law360
March 22, 2024
Ninth Circuit Affirms Class Certification Against Meta Platforms
Consumer class action addresses Meta Platforms fraudulently misleading advertisers with inflated metrics about “potential reach.” WASHINGTON, DC– The United States Court of Appeals for the Ninth Circuit affirmed a district court’s 2022 order certifying a class of advertisers who paid Meta Platforms, Inc. (Meta) to place advertisements on its social media platforms (the damages class). […]
Press Releases | Cohen Milstein