The Ontario Public Service Employees Union (OPSEU; French: Syndicat des employés de la fonction publique de l'Ontario [SEFPO]) is a trade union representing public sector employees in the province of Ontario, Canada.

Additionally, some members work for private companies or organizations that are contracted to provide a public service such as hospitals and medical laboratories.

The list of bargaining units includes Colleges of Applied Arts & Technology - Academic (CAAT-A) with about 12,000 members, just under 10% of OPSEU's total membership, Colleges of Applied Arts & Technology - Support (CAAT-S), Hospital Professionals Division Central Provisions (HPD), Liquor Control Board of Ontario (LCBO), Municipal Property Assessment Corporation (MPAC), Ontario Public Service (OPS).

Other members include ambulance, developmental services, boards of education, children's aid societies, community agencies, long-term care, universities, hospital professionals, hospital support, municipalities, child treatment centres, municipal property assessment, mental health, Canadian Blood Services and Diagnostics.

Ontario Provincial Police riot control officers were called in to escort members of parliament who were being prevented from entering the legislature.

[16] The strike ended on November 14 when OPSEU and the Ontario Council of Regents agreed to binding arbitration after back-to-work legislation was threatened.

At the time, full-time faculty had "a starting salary of about $32,000, an average pay of about $75,000 and a 16-year progression to reach top wage levels in their collective agreement, according to the union.

[21] The OPSEU collective bargaining team for the teachers was led by J.P. Hornick, Coordinator of the School of Labour at George Brown College.

[22][23] Bill 178, the Colleges of Applied Arts and Technology Labour Dispute Resolution Act, 2017 was successfully passed on Sunday, November 19, 2017, ending the strike and sending the parties to mediation and binding arbitration.

[27] The decision included a 7.75 increase in wages over four years and a one time lump sum payment for full and part-time staff.

In January 2023, OPSEU launched a lawsuit against Thomas and two executives who served under him alleging that they had misappropriated just under $6 million in union funds.