Margaret H. Allen

MARGARET ALLEN is the co-leader of Sidley’s Labor, Employment and Immigration practice who represents companies in high-stakes employment and civil rights matters. Margaret is a go-to advisor to executives and boards due to her business-minded approach and commitment to client success. She regularly advises employers on complex employment issues, including whistleblower claims and sensitive executive matters.

In addition to her employment law focus, Margaret also has extensive experience in internal investigations and enforcement actions involving the Department of Justice, the Securities and Exchange Commission, and many other federal and state agencies.

Margaret also represents employers and executives in complex commercial litigation, including class actions, multi-jurisdictional disputes, and high-risk business litigation involving breach of contract, business torts, and securities claims. Her litigation experience covers all phases of cases, from pleadings and discovery to trial and appeal, in both U.S. courts and arbitration forums.

Margaret’s experience and client service have earned her recognition by Chambers USA for Texas Labor & Employment (2021–2025), where clients describe her as “a sharp, smart and savvy litigator,” “a strong advocate for her clients,” and “a tough negotiator” with strong commercial instincts. She has also been named a “Future Star” (2023–2025) and “Labor & Employment Star” (2022) by Benchmark Litigation.

Margaret also brings valuable international experience, having worked in Singapore, where she advised multinational companies on cross-border employment and investigatory matters.

A sampling of Margaret’s experience at and prior to joining Sidley includes:

• Represented board committee of public company in investigation of whistleblower claims brought by C-suite executives alleging harassment and discrimination by the CEO.
• Represented numerous public and private company C-suite officers in negotiating their exits to maximize equity and bonus payouts.
• Represented board committee of public corporation in U.S. agency investigation involving alleged violations of Foreign Corrupt Practices Act.
• Numerous internal investigations involving whistleblower, accounting, and executive issues.
• Represented importing company in investigating former employee’s illegal hacking and cybersecurity violations.
• Won at trial (including all attorneys’ fees) against former employee who stole trade secrets and violated the Computer Fraud and Abuse Act through hacking and engaging in cybersecurity violations.
• Represented public company in responding to subpoena and inquiry by Office of Special Investigations of the United States Air Force related to potential False Claims Act issues.
• Won complete dismissal with prejudice of Sarbanes-Oxley (SOX) whistleblower claims against publicly-traded company.
• Successfully obtained dismissal and negotiated resolution of numerous sexual assault allegations against publicly-traded company across the U.S.
• XRI Investment Holdings LLC – XRI Investment Holdings LLC v. Holifield (Delaware) – Won trial verdict against former founder who fraudulently transferred his equity interests in violation of company agreement. Affirmed by the Delaware Supreme Court.
• Charter Communications — Castorena v. Charter; Prizler v. Charter; Moorman v. Charter (California, Wisconsin) — Won motions to compel arbitration and to stay numerous nationwide class actions pending in California and Wisconsin.
• Nevro Corp. — Nevro Corp. v. Olson (Texas) — Obtained temporary restraining order and temporary injunction to enforce noncompetition and nonsolicitation obligations against former employee who joined a competitor.
• Apache Holdings — Apache IS Holdings, LLC v. Thibodeaux (Louisiana, Texas) — Won motion to enforce mandatory venue provision and dismissal of entire Louisiana action.
• Federation of State Medical Boards — Federation of State Medical Boards v. Day (Texas) — Obtained complete dismissal of physician’s defamation claims under Texas Citizens’ Participation Act, aka Texas’ anti-strategic lawsuit against public participation statute, as well as award of all attorneys’ fees. Affirmed on appeal.
• Hewlett Packard — Benedict v. Hewlett Packard (California) — Defeated class certification in exempt status class action under Fair Labor Standards Act and related state statutes originally brought on behalf of over 16,000 technical solutions professionals.
• American Airlines — Woodall v. American Airlines, Inc. (Texas) — Lead trial counsel for American in putative class action brought by the Civil Rights Division of the U.S. Department of Justice under the Uniformed Services Employment and Reemployment Rights Act.
• General Motors — In re Motors Liquidation Co. (New York) — Successfully obtained discharge in bankruptcy proceedings of all putative class action claims against successor to General Motors Corporation, including claims under the Alien Tort Claims Act brought on behalf of a putative class consisting of all black South Africans who were victims of Apartheid.
• General Motors — In re Motors Liquidation Co. (New York) — Successfully settled over US$1 billion of unliquidated claims against debtor’s estate by setting up a cutting-edge, court-ordered alternative dispute resolution program. Mediated and settled dozens of cases nationwide.
• Negotiations against Texas Juvenile Justice Department (Texas) — Collaborated with Texas Appleseed to negotiate, through a series of written submissions and agency meetings, improvements to mental health and education policies for imprisoned children, including the improper use of solitary confinement.
• Zale Corporation (Texas) — Represented Zale in class actions brought under the Securities Exchange Act of 1934. Won early dismissal with prejudice, later affirmed by the Fifth Circuit.
• American Airlines — American Airlines, Inc. v. Sabre Inc. and Travelport (Texas) — Represented American in lawsuits brought in state and federal courts against the two largest global distribution systems for breach of contract, tort claims, and antitrust violations under state and federal laws. Negotiated an extremely favorable settlement following voir dire and six days of trial.
• Deutsche Bank, Barclays Bank, and Commerzbank AG (California, France) — MGA Entertainment Inc. v. Deutsche Bank, et al. — Won motion to dismiss US$429 million fraud action against clients Deutsche Bank and other syndicate banks on grounds of forum non conveniens.
• Alliant Insurance Services (California, New York) — Represented Alliant in parallel lawsuits pending on opposite coasts involving allegations of misappropriation of trade secrets and aiding and abetting breaches of fiduciary duty related to the departure of a group of 60 Aon employees for Alliant.
• HM Capital (Texas, Utah, Alaska) — Litigation counsel for portfolio companies of HM Capital in internal investigation that led to successful injunction against whistleblower and ultimate dismissal of two separate class action complaints alleging breach of contract and torts related to distribution of telephone directories.
• Medical Media Holdings, LLC (Texas, Colorado, and before arbitration panel) — Physicians’ Education Resource, L.P. v. MMH, LLC — Trial counsel for portfolio company of private equity fund in several trade secret misappropriation and restrictive covenant matters. Successful results affirmed by the Dallas Court of Appeal.
• kgb/USA — Jingle Networks v. InfoNXX, Inc. (Texas, Massachusetts, and before arbitration panel) — Litigation counsel for kgb in several overlapping and related matters involving noncompete, breach of contract, and defamation claims.
• In re Stanford (Texas) — On behalf of a large financial institution, successfully negotiated return of fleet of five securitized personal jets allegedly worth over US$100 million in wake of uncovered Ponzi scheme.
• McAfee, Inc. — John Giamatteo v. AVG Technologies USA, Inc. (Massachusetts, California) — Trial counsel in multi-state noncompete litigation. Defeated TRO and obtained favorable settlement.
• J.C. Flowers & Co. (Delaware, Canada, United Kingdom, Cayman Islands) — In re HCH Delaware L.P. — Represented portfolio company of private equity firm in converting involuntary proceedings brought in the Cayman Islands by a syndicate of lenders to a Chapter 11 voluntary matter. Negotiated settlement following filing of restructuring proceeding.
• Represented VIO Med Spa (VIO), a franchisor of full-service med spas, in its majority investment from Freeman Spogli.

Margaret is a director with the Northwestern Pritzker School of Law Fund Board and a fellow with the Dallas Young Lawyers Foundation.

Margaret also serves on the board of Texas Appleseed, a nonprofit organization dedicated to promoting social, economic, and racial justice for all Texans by leveraging the skills and resources of volunteer lawyers, other professionals, and community partners to identify practical solutions to difficult, systemic problems.