The sponsors claim it's to cut down on dog bites but it sounds more like a PETA "free the animals" kind of thing. From KCRA TV:
The state Senate on Thursday approved a bill that would prohibit the chaining of dogs to a stationary object, such as a tree or fence, as a primary means of confinement.According to a news release from the California Animal Association, which sponsors the bill, the legislation was originally introduced as a public safety measure to reduce the number of dog bites and dog attacks.
The group said research has shown that chained dogs are 2.8 times more likely to bite than unchained dogs.