Organizational and organisational are both English terms.
Organizational is predominantly used in 🇺🇸 American (US) English (en-US) while organisational is predominantly used in 🇬🇧  British English (used in UK/AU/NZ) (en-GB).
In terms of actual appearance and usage, here's a breakdown by country, with usage level out of 100 (if available) 👇:
| Term | US | UK | India | Philippines | Canada | Australia | Liberia | Ireland | New Zealand | Jamaica | Trinidad & Tobago | Guyana | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| organizational | 99 | 29 | 57 | 99 | 95 | 23 | 100 | 37 | 34 | 89 | 77 | 74 | 
| organisational | 1 | 71 | 43 | 1 | 5 | 77 | 0 | 63 | 66 | 11 | 23 | 26 | 
Below, we provide some examples of when to use organizational or organisational with sample sentences.
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license.)