| U a Local 67M C a Zone 9/9A Apprenticeship Committee | Other Public Sector Employers | 2017 | 1 | $115,283 |
| UA Local 67/MCA Zone 8/9/9A Apprenticeship Committee. | Other Public Sector Employers | 2016 | 1 | $105,536 |
| Ukrainian Canadian Care Centre | Other Public Sector Employers | 2025 | 8 | $116,744 |
| Ukrainian Home for the Aged | Other Public Sector Employers | 2017 | 1 | $124,880 |
| Ukrainian Home for the Aged – Ivan Franko Homes | Other Public Sector Employers | 2012 | 1 | $115,351 |
| Unemployed Help Centre of Windsor | Other Public Sector Employers | 2025 | 5 | $113,027 |
| Unemployed Help Centre of Windsor Inc. | Other Public Sector Employers | 2009 | 1 | $104,483 |
| Union of Ontario Indians | Other Public Sector Employers | 2025 | 3 | $121,971 |
| Unionville Home Society | Other Public Sector Employers | 2025 | 11 | $137,719 |
| Unison Health and Community Services | Other Public Sector Employers | 2025 | 39 | $177,128 |
| Unite Here Local 75 | Other Public Sector Employers | 2025 | 2 | $145,000 |
| United Association 67 Technical Trades Academy Inc | Other Public Sector Employers | 2015 | 1 | $105,511 |
| United Brotherhood of Carpenters and Joiners of America Local 2486 | Other Public Sector Employers | 2024 | 3 | $112,788 |
| United Brotherhood of Carpenters Local 785 Building Corporation | Other Public Sector Employers | 2025 | 1 | $108,436 |
| United Chiefs and Councils of Manitoulin Police Services Commission | Other Public Sector Employers | 2022 | 2 | $126,283 |
| United Chiefs and Councils of Mnidoo Mnising | Other Public Sector Employers | 2023 | 1 | $112,224 |
| United Church of Canada in Ontario | Other Public Sector Employers | 2011 | 1 | $120,000 |
| United Counties of Leeds and Grenville | Municipalities & Services | 2025 | 95 | $119,490 |
| United Counties of Prescott and Russell | Municipalities & Services | 2025 | 146 | $121,690 |
| United Counties of Stormont, Dundas and Glengarry | Municipalities & Services | 2025 | 17 | $133,253 |
| United for Literacy | Other Public Sector Employers | 2025 | 4 | $138,858 |
| United Mennonite Home for the Aged | Other Public Sector Employers | 2025 | 9 | $123,850 |
| United Townships of Dysart , Dudley, Harcourt, Guilford, Harburn, Bruton, Havelock, Eyre & Clyde | Municipalities & Services | 2012 | 1 | $101,844 |
| United Way Canada - Centraide Canada | Other Public Sector Employers | 2008 | 5 | $135,766 |
| United Way of Canada - Centraide Canada | Other Public Sector Employers | 2009 | 5 | $135,352 |
| Unity Health Toronto | Hospitals & Boards of Public Health | 2025 | 2,896 | $125,107 |
| Universite de l'Ontario Francais | Universities | 2025 | 55 | $139,672 |
| University Health Network | Hospitals & Boards of Public Health | 2025 | 4,581 | $131,064 |
| University of Guelph | Universities | 2025 | 1,504 | $164,997 |
| University of Ottawa | Universities | 2025 | 2,861 | $158,196 |
| University of Ottawa Health Services Family Health Team | Other Public Sector Employers | 2020 | 2 | $118,969 |
| University of Ottawa Heart Institute | Hospitals & Boards of Public Health | 2025 | 530 | $125,442 |
| University of Saskatchewan | Other Public Sector Employers | 2022 | 2 | $155,000 |
| University of St. Jerome's College | Universities | 1996 | 1 | $146,414 |
| University of St. Michael's College | Universities | 2025 | 40 | $164,084 |
| University of Sudbury | Universities | 2025 | 2 | $178,640 |
| University of Toronto | Universities | 2025 | 7,392 | $171,936 |
| University of Waterloo | Universities | 2025 | 2,376 | $167,162 |
| University of Western Ontario | Universities | 2025 | 1,963 | $166,269 |
| University of Windsor | Universities | 2025 | 929 | $155,074 |
| Université de Hearst | Universities | 2025 | 30 | $126,707 |
| Université Saint-Paul / Saint Paul University | Universities | 2013 | 6 | $105,326 |
| Unt'd Cties-Stormont, Dundas, Glengarry | Municipalities & Services | 2005 | 3 | $114,208 |
| Untd. Counties of Stormont, Dundas & Glengarry | Municipalities & Services | 2006 | 3 | $109,348 |
| Up With Women | Other Public Sector Employers | 2025 | 1 | $155,000 |
| Upper Canada District School Board | School Boards | 2025 | 1,433 | $122,759 |
| Upper Canada Family Health Team | Other Public Sector Employers | 2023 | 3 | $122,467 |
| Upper Canada Leger Centre for Education & Training | Other Public Sector Employers | 2012 | 1 | $104,543 |
| Upper Canada Leger Centre for Education and Training | Other Public Sector Employers | 2025 | 3 | $121,443 |
| Upper Grand District School Board | School Boards | 2025 | 1,805 | $121,631 |
| Upper Grand Family Health Team | Other Public Sector Employers | 2023 | 3 | $107,413 |
| Upper Thames Conservation Authority | Other Public Sector Employers | 2016 | 2 | $118,123 |
| Upper Thames River Conservation Authority | Other Public Sector Employers | 2025 | 17 | $127,374 |
| Upsala District School Area Board | School Boards | 2008 | 1 | $108,634 |
| Upsala District School Authority | School Boards | 2006 | 1 | $101,929 |
| Upstream Ottawa Community Mental Health Support | Other Public Sector Employers | 2025 | 1 | $116,760 |
| Urban Rez Solutions | Other Public Sector Employers | 2018 | 1 | $100,000 |
| Urban Rez Solutions Social Enterprise | Other Public Sector Employers | 2025 | 2 | $108,307 |