Impermissible (adjective)

1. Not allowed or permitted; prohibited.
2. Not acceptable; not conformable to a rule or standard.

Origin:

Mid 19th century: from in- "not" + permissible.

Examples:

1. The action is impermissible according to company policy.
2. The behavior was considered impermissible and unacceptable.
3. The use of certain words is impermissible in the classroom.
4. The plan was rejected as it was deemed impermissible under the laws and regulations.
5. The activity was considered impermissible due to safety concerns.