* "dis-" for the opposite of allow, meaning "not allow" or "prohibit" (e.g., disallow, disapprove).
* "un-" can also indicate the opposite of allow, especially when talking about something being permitted (e.g., unpermitted, unauthorized).
* "pre-" can be used to suggest something allowed in advance (e.g., pre-approved, pre-authorized).
* "per-" is often used to indicate permission or allowing (e.g., permissible, permitted).
The best prefix to use depends on the specific meaning you want to convey.