You can call Tesla too. This is from their supercharger FAQ. "A non-Tesla car is parked in a dedicated Supercharger stall, what should I do?
Please notify Tesla at (877) 798-3752."
Maybe we should call every time there is an ICE in the stall, not just when we don't have a spot to charge at. That way they know how serious the issue is.
According to Tech Crunch the agreement with Tesla for the Supercharging Partners program is that the parking spots are to be dedicated to Tesla cars. Now, what that means as far as towing, cones, etc. isn't at all clear, at least to me, so while there is an agreement, it may not have any practical effect.
From what I've seen, a lot of public Level 2 chargers have the same ICEing problems as well. Without any incentive to do otherwise, it seems likely that ICE drivers and parking space owners in many cases won't keep charging spaces free for BEV's.
This all really does raise some questions about the real utility of the Supercharging network as more Teslas are sold. While Supercharging will help a lot with range anxiety, if owner's experiences involve frequent significant waits for others charging and/or ICEing there may be a lot of public questioning about their practicality as primary transportation.
That article is from July and given that we are starting to see general parking/supercharger signs being installed at the newer locations I suspect that the agreement has changes somewhat.
I just wanted to emphasize the point rlang59 makes. Tesla have what they call Dedicated parking and Enabled parking. As the name suggests Dedicated parking is dedicated to Tesla vehicles. Enabled parking are Supercharger stalls shared with non-Teslas, including gasoline vehicles. The Enabled spots are undoubtedly dictated by the host location and enforcement can vary from site to site.
Here's a photo of Florida's Enabled parking.
Larry