Jeffrey Sack, K.C. practices labour law and acts as a union nominee on interest arbitration boards. As a litigator he argued the Lavigne case in the Supreme Court of Canada, which upheld the constitutional validity of the Rand (agency) formula and (contrary to U.S. jurisprudence) confirmed the right of unions to use union dues for political causes. He also argued the first case upholding the right to strike under the Canadian Charter of Rights and Freedoms, which was relied upon by the Supreme Court of Canada in its recent Saskatchewan Federation of Labour decision.

As a negotiator, Jeffrey has bargained with the government for physicians, and with hospitals for residents. As a union nominee on interest arbitration boards he has represented, among others, firefighters, police officers, college and university faculty, and health care support staff. As an adjunct professor, he lectures on international labour law at the University of Toronto and acts as Associate Editor of the Canadian Labour and Employment Law Journal.

Jeffrey is the recipient of the Gérard Dion Award from the Canadian Industrial Relations Association (CIRA) for major contributions to Canadian labour law and of the Outstanding Practitioner Award from the U.S. Labor and Employment Relations Association (LERA).