Our group (IT) has been functioning well for several years with few incidents and none worth mentioning.
The problem: Recently, we've had someone from a different group, who is a super-user, and pretty far up in the food chain in his group, interfering with our operations.
Our own manager is fairly new and has less time with the company than "Super User" and "Super User" has been trying to throw his weight around due to fact that he is senior and knows a bit of what we are doing. He is technically higher up in the ranking than our manager.
While "Super User" is very competent in his role, he thinks (and acts) like his competence translates to our group, and our manager is tired of playing games.
Naturally, this has had double the effect on morale as it is affecting our manager and our team as well. It's bad because "super user" is extremely rude to our manager. I even heard him insult our manager to his face.
What can our manager do, or we as a team do, to stop the interference of a more senior manager from another department?