I'm looking for a noun or adjective noun combination that, as clearly as possible, explicitly identifies employees that don't have anyone reporting to them.
The closest existing question I could find was A word for people who work under a manager and it doesn't help me because people who fit that description are not precluded from having subordinates of their own.
Required example: We categorize employees as upper management when they report only to the board of directors. Middle management personnel report to another employee and also have employees reporting to them. [some noun or adjective noun combo] are employees that have no subordinates in the company.