| A & M Tornio Avoin Yhtiö | Wholesale & retail | 2006 |
| A&B Huhtaset OY | Construction | 2025 |
| A&K Rakennuttajat Oy | Construction | 2010 |
| A.Isto Invest Oy | Financial services | 2021 |
| A1 Autokuljetus Oy | Transport & logistics | 1975 |
| A1 Autopalvelu Oy | Transport & logistics | 1976 |
| AK Yhtiöt Oy | Wholesale & retail | 2008 |
| AKK Group Ky | Other services | 2004 |
| AMF Konemiespalvelut Oy | Administrative & support | 2023 |
| AML-Service Oy | Professional & scientific | 2026 |
| AN Maskinteknik Finland Oy | Wholesale & retail | 2020 |
| ATJ Kiinteistöt Oy | Real estate | 2020 |
| ATK-Palvelu Jukka Ollitervo Ky | Information & communication | 1994 |
| AURQON Capital Oy | Financial services | 2025 |
| Aapeli Yhtiö Oy | Hospitality | 2023 |
| Aapo Ylimäki Oy | Administrative & support | 2024 |
| Aatos Capital Oy | Real estate | 2018 |
| Aava-Rakennus Oy | Construction | 1990 |
| Aavasaksan Sähkö Oy | Construction | 2018 |
| Achilles Lines Oy | Transport & logistics | 2008 |
| Advox Lakitoimisto Bergman Oy | Professional & scientific | 2024 |
| AeroExcellence Oy | Hospitality | 2026 |
| Ahkio Arctic Oy | Professional & scientific | 2022 |
| Ahotrans Oy | Transport & logistics | 1978 |
| Aineximp Alpo Aine Ky | Wholesale & retail | 1990 |
| Ala LKV Oy | Real estate | 2024 |
| Alakap Oy | Real estate | 2024 |
| Alakuijala Oy | Construction | 1987 |
| Alapon Oy | Real estate | 2024 |
| Alaraumon Maalaamo A Friman Ky | Other services | 1984 |
| Alaven Oy | Professional & scientific | 2013 |
| Alfa Ratkaisut Ky | Professional & scientific | 2012 |
| All Wörks Oy | Manufacturing | 2022 |
| Alppinäppärät Oy | Real estate | 1996 |
| Altiplan Oy | Health & social care | 2007 |
| Ama Products Oy | Manufacturing | 2025 |
| Ammatillinen perhekoti Olsen Ky | Health & social care | 2008 |
| Aninka Dialogues Oy | Health & social care | 2024 |
| Ankome Oy | Manufacturing | 2021 |
| Anspe Oy | Real estate | 2017 |
| Antimoney Oy | Financial services | 2025 |
| Antti Kaarlela Oy | Wholesale & retail | 2008 |
| Antti Ponkala Oy | Transport & logistics | 2007 |
| Arctic Action Oy | Arts & recreation | 2015 |
| Arctic Fox Production Oy | Arts & recreation | 2023 |
| Arctic Lynx Capital Oy | Financial services | 2025 |
| Arctic Paint Oy | Construction | 2020 |
| Arctic Property Oy | Real estate | 2013 |
| Arctic Rabbit Oy | Construction | 2018 |
| Arctic Sauna Oy | Construction | 2024 |
| Arctic Steel Oy | Manufacturing | 2011 |
| Arctic Tec Oy | Manufacturing | 2015 |
| Argillander Management Oy | Professional & scientific | 2022 |
| Arjen Kaverit OY | Other services | 2026 |
| Arkkitehtitoimisto Arkture Oy | Professional & scientific | 1987 |
| Arkunnaula Oy | Professional & scientific | 2022 |
| Aromtech Oy | Manufacturing | 1991 |
| Arpela Fund I Oy | Professional & scientific | 2025 |
| Arpela Fund II Oy | Professional & scientific | 2025 |
| Arpelan Tilitoimisto Oy | Professional & scientific | 2002 |
| Arpelan Vesiosuuskunta | Water & waste | 1969 |
| Arpelan konepaja oy | Manufacturing | 2026 |
| Art Idea Oy | Construction | 2021 |
| Arvokanava Oy | Real estate | 2025 |
| Asennus Pirttimaa Oy | Construction | 2023 |
| Asianajotoimisto HP Laki Oy | Professional & scientific | 2017 |
| Asianajotoimisto Hannu Melaluoto Ky | Professional & scientific | 1985 |
| Asianajotoimisto Heikki Huhtanen Ky | Professional & scientific | 1996 |
| Asianajotoimisto Jarmo Raappana Oy | Professional & scientific | 2021 |
| Asianajotoimisto Paul Henriksson Ky | Professional & scientific | 1984 |
| Asianajotoimisto Reetta Keskitalo Oy | Professional & scientific | 2021 |
| Asianajotoimisto Tuomo Heikkilä Oy | Professional & scientific | 2019 |
| Asumisaamu Oy | Health & social care | 2019 |
| Audinex Oy | Wholesale & retail | 2025 |
| Aurora Tornio Oy | Energy | 2013 |
| Auto Helander Ky | Other services | 2008 |
| Auto- ja pienkonehuolto Tryyki Oy | Other services | 2023 |
| Autodek Oy | Manufacturing | 1998 |
| Autohuolto Cool Special Ky | Other services | 2004 |
| Autokorjaamo J.Juopperi Ky | Other services | 2008 |
| Autokorjaamo P. Mäkinen Oy | Other services | 2011 |
| Automaalaamo V Ponkala Kommandiittiyhtiö | Other services | 1980 |
| Autopalvelu Ojanperä Oy | Wholesale & retail | 1996 |
| Autosähkö & Kalastusopas JL Ky | Other services | 2009 |
| Autotarvike Kuukasjärvi Oy | Wholesale & retail | 2003 |
| Avec Creative Oy | Other services | 2022 |
| Avoin Yhtiö Tornion Muotipuoti | | 1988 |
| Avoin yhtiö Tornion Ruokamarkkinat | | 1998 |
| Bestpipe Ky | Manufacturing | 2002 |
| Betonggruppen Finland Oy | Manufacturing | 2025 |
| BioTermo Oy | Energy | 2010 |
| Bonus Remontit Oy | Construction | 2016 |
| Boreal Paint Oy | Manufacturing | 2019 |
| Botnia Trotters Oy | Financial services | 1988 |
| Botnium Oy | Real estate | 2002 |
| BroBusiness Oy | Professional & scientific | 2023 |
| Business Tornio Oy | Public administration | 1999 |
| Canoteam OY | Wholesale & retail | 2007 |
| Cafe Katariina Oy | Hospitality | 2012 |
| Cafe Rohkifiini Oy | Hospitality | 2012 |