Internally, the support system has five priorities: Low, Medium, High, Urgent and Critical.
All users start out as standard-level users.
When a standard-level user is creating a support ticket, they have access to three priorities: High, Urgent and Critical. Once a ticket has been submitted, the system will silently map the priority indicated by the user into an internal priority. For a standard-level user, it goes High->Low, Urgent->Medium, and Critical->High. It's still three levels of priority, but the internal names reflect how IT will look at them, while the external names reflect how the users see them.
If a standard-level user asks for the ability to report tickets for things which are lower priority than High, Urgent or Critical, because they have issues they'd like to log which they do not consider to be "High" priority, then that user is converted to a second-level user.
When a second-level user is creating a support ticket, they have access to four priorities: Medium, High, Urgent and Critical. Once this ticket has been submitted, it will be translated internally from Medium->Low, High->Medium, Urgent->High, and Critical->Urgent. Thus, because a second-level user has shown that they have an understanding of what lower priority levels are for, the priority levels of their tickets are taken more seriously than those of standard-level users.
If a second-level user asks for the ability to report tickets for things which are "Low" priority, because they do not feel comfortable reporting unimportant things as "Medium" then that user is converted to third-level. Third level users have access to the full range of Low, Medium, High, Urgent and Critical priorities when reporting tickets, and their priorities are not re-mapped internally.
Optionally, the system could also include a zero-level user type, to accommodate users who complain that "Critical" is not a high enough priority level to properly represent the issues they're having. Those users would be given access to "High", "Urgent", "Critical", and "Ultra" priority levels. Internally, those would be converted to "Low", "Low", "Medium" and "Medium" respectively.