This is the conclusion of attorneys who are analyzing the legal consequences of the initiative for agricultural and food interests in California, whose "Californians for SAFE Food" coalition is organised to educate Californians on the initiative and urge them to vote no on the measure.

The determination makes it exceedingly important for producers and production companies, trade associations and allied industry across the US to become involved in the "SAFE Food" coalition, its supporters said.

The initiative - which has been designated "Proposition 2," or "Prop 2" - is directed at the treatment of farm animals and, if passed, would require that farm animals not be confined or tethered in a manner that prevents an animal from lying down, standing up, turning around and fully extending its limbs.

For a hen in an egg production system, fully extending its limbs means extending its wings without touching the side of an enclosure, such as a cage, or another hen, according to the initiative.

The initiative is directed at cage housing systems for hens and sow and veal calf stalls, but recent studies found that even most barn, or cage-free, housing systems for hens would be prohibited under the requirement.

The law would become effective on 1 January 2015, and would carry penalties for violations of a fine not to exceed $1,000 and/or a jail term not to exceed 180 days. Legal observers have said violations could cover each animal.

Normally in California investigations surrounding and arrests for alleged violations of criminal statutes are conducted by law enforcement and prosecutorial authorities.

However, in a paper based on legal opinion, it was noted that California law is unique in that enforcement of animal cruelty and welfare laws "can be undertaken and/or compelled by any individual or by certain non-profit organisations".

The paper quoted California Penal Code 599a, which provides that an individual, who can represent a non-profit organization, can compel issuance of search warrants upon making a complaint under oath.

When such a complaint is made to any magistrate authorised to issue warrants that the complainant believes that any law relating to, or in any way affecting, "dumb animals or birds is being, or is about to be, violated in any particular building or place", that magistrate must issue a warrant to any law enforcement officer or to an officer of a legally qualified association "authorising him to enter and search that building or place and to arrest any person there violating, or attempting to violate" the law, according to the paper's summation of the penal code.

The initiative qualified for the ballot through a petition carried by animal activists led by Farm Sanctuary and the Humane Society of the United States (HSUS), both non-profit organisations.

Accordingly, the paper suggested that any representative of Farm Sanctuary, HSUS or other animal activist group "would be free to demand and execute warrants and make arrests" to enforce the initiative, the paper said.

The empowerment of non-profit organisations to enforce California animal cruelty laws is further provided for in California Corporations Code Sections 10400 and 14502, the paper said, noting that representatives of such organisations can obtain "peace officer" powers with respect to animal welfare laws.

This unique enforcement feature is almost never referred to by supporters of Prop 2 and is not ordinarily understood by the voting public, the paper said.

In a statement, senior campaign director for "SAFE Food" Mitch Head said Prop 2 would establish a precedent for the enforcement of animal welfare laws.

"This is something that all of American agriculture must realise," he said, explaining how Prop 2 would help the animal activist groups supporting the measure "not only increase their political powers but also their police powers".