jur

I wonder if someone complained to the manager; why would he go through the hassle in the first place?

Bike racks can be quite dangerous; my own hitch-mounted rack when no bikes are mounted can cause serious cuts when walking into it, that happens sometimes with myself since I am usually looking down at the ground and the rack is at head height.

So make sure it is not hazardous by hanging some safety ribbon or whatever from it when parked, and make sure the car is in as far as it will go so that the rack is really out of the way. In Australia it is actually illegal to drive around with an unloaded bike rack.

Finally, check what the law wrt bike racks say. If you're OK, fall back on those laws. With a lawyer. If he is really difficult AND legally you're OK, promise him you will charge him with grand theft if he removes your car without permission.

[edit] Could you simply remove the rack? All racks I know of are easily removed.