Can a trailer park charge for an untagged car?

I have a friend who has a car that is currently missing its renewal sticker, she cannot drive it as she has a suspended license, tag has been renewed and she simply has lost the sticker, and she will be going to get a new one as soon as she can, but in the meantime the trailer park where the car is parked at her trailer, the management is threatening to charge her $25/hr unless she moves the car or gets the tags renewed. Is this even legal? I can understand if they had it towed, but charging by the hour seems a little bit unlawful/excessive.