A proposal that would ban modern housing systems for egg-laying hens, veal calves and gestating sows by 2015 was approved Tuesday by California voters.

Florida, Arizona, Colorado and Oregon have passed similar laws for swine and veal. California, however, becomes the first state to require that all egg-producing chickens be kept in more spacious enclosures or free to roam a henhouse. Most pig and veal farmers in the state have already expanded their pen sizes. As a result, the law’s requirements will have the most significant impact on poultry farmers.

Supporters of Proposition 2 said the initiative would guarantee farm animals a better life, giving them the space they need to stand up, turn around, lie down and extend their wings, as well as prevent diseases caused by overcrowding.

Opponents argue that the cost of the measure threatens California's egg industry and may force California livestock and poultry operations into other states or put some out of business.

In approving the initiative, voters rejected the arguments of Gov. Arnold Schwarzenegger, the agriculture industry and the American Veterinary Medical Association (AVMA).

In response to passage, AVMA CEO Ron DeHaven, DVM, said, “Now that the ballot initiative has passed, veterinarians and animal welfare scientists must be involved in its implementation to make sure that resulting changes in animal housing actually improve conditions for the animals they are intended to help. If we're not careful, animal health and welfare problems could be precipitated that are as significant as the concerns Proposition 2 aspires to address.”