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John Mastoras

Senior Partner

John  Mastoras


T:+1 416.216.3905

John Mastoras is a senior partner in our Canadian employment and labour law group. He is known to clients as a passionate and dedicated advocate and business partner who provides innovative and practical advice.

John is frequently called upon to litigate highly contentious matters such as disruptive labour disputes and workplace mental health issues, and acts exclusively for employers in the broader area of labour and employment law. He regularly litigates and provides strategic advice in connection with labour arbitrations, labour relations board disputes, human rights proceedings, occupational health and safety charges, workers' compensation, labour injunctions and common law employment actions. His practice spans union and non-union workplaces for both federally and provincially regulated employers.

John is often in the forefront as chief spokesperson in collective bargaining and provides helpful counsel in this regard to a variety of employers. He routinely acts for a broad group of employer clients  and employer associations in various industries and sectors, including energy, pulp and paper, pharmaceutical, health care, education, longshoring, construction, retail, food processing, transportation, steel, automotive and manufacturing more generally.

For the past 20 years, John has taught at the University of Toronto's Centre for Industrial Relations and Human Resources (CIRHR), where he is an Adjunct Professor. In 2009, John was conferred the Morley Gunderson Prize by the University of Toronto as a CIRHR graduate who combines outstanding professional achievement with significant service to the university.

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  • Education
    • LL.B., Osgoode Hall Law School, 1987
    • M.I.R., University of Toronto, 1984
    • B.A.(Hons.), University of Toronto, 1981
  • Admissions
    • Ontario 1989
  • Rankings and recognitions
    • Chambers Canada, Ontario: Employment and Labour, Chambers and Partners, 2018
    • Best Lawyers in Canada (2015-2017): Labour and Employment Law
    • Canadian Legal Lexpert Directory (2012-2017): recommended in Workers' Compensation - Employer
    • Canadian Legal Lexpert Directory (2016): recommended in Labour Relations - Management
    • PLC Which lawyer? (2011): Labour and employment
  • Publications
    • "You Can't 'Juke' the Collective Agreement's Exclusive Jurisdiction," Employment and Labour Law Reporter, May 2016 Volume 26, No. 2
    • "Mexican officials improperly interfered in union representation vote" (co-author), Canadian section, Brussels European Employee Relations Consultants (BEERG) and HR Policy Association, May 2014.
    • "Supreme Court rules random alcohol testing not permitted without evidence of a significant workplace problem" (co-author), Brussels European Employee Relations Consultants (BEERG) and HR Policy Association, February, 2014.
  • Speaking engagements
    • "Relationships with Non-Bargaining Unit Employees," Conference Board of Canada, Council of Industrial Relations Executive, June 15, 2017
    • "Ontario's Changing Workplaces Review," Norton Rose Fulbright Annual Workplace Law Conference, May 17, 2016
    • "Representation Elections in Canada – How Does a Speedier Election Process Work in Practice?" U.S. Labor and Employee Relations Network, May 14-15, 2014
    • "Navigating the Legal Highway: Recent Labour and Employment Developments," Ontario Trucking Association, February 13, 2008
  • Memberships and activities
    • Canadian Bar Association
    • Law Society of Upper Canada
    • The Advocates' Society
    • HR Policy Association (US)  
    • American Bar Association