What is the name of your state (only U.S. law)? California

I live in a mobile home park in Hesperia, CA. We moved into this park in January 2007. At the time we moved in, we informed the current management of our pets, which included a black lab and a long haired chihuahua. The manager at the time inquired about the size of the lab. She was told his size, shown a picture, and informed of his personality. There was never any other issue concerning that dog. Now, 2 1/2 years later, that manager is no longer employed here and the mobile home park owner has been filling in. Yesterday I found a note posted to my front door that states the we have a pet violation; Pet is greater than the maximum weight allowed in the community. It says that the dog "must go immediately" and that failure to comply will result in termination of our tenancy.
How can he legally go back on something that has been accepted as "past practice" over 2 years later? I've had my dog for 7 years, he is like family.