Cal. Ins. Code § 11656.5

In order to permit employees of small farms to be brought under the provisions of the Workers’ Compensation Law, employers of agricultural labor who are members of any nonprofit agricultural association or who are members of, or stockholders in, any nonprofit cooperative agricultural marketing association of producers, some or all of whom may not be required to carry compensation insurance, may, under such conditions as the commissioner may prescribe in order to effectuate the purpose of Article 2, Chapter 3, of this part, be insured under a group compensation insurance policy.