California Code, Labor Code - LAB § 3360

Workmen associating themselves under a partnership agreement, the principal purpose of which is the performance of the labor on a particular piece of work are employees of the person having such work executed.  In respect to injuries which occur while such workmen maintain in force insurance in an insurer, insuring to themselves and all persons employed by them benefits identical with those conferred by this division the person for whom such work is to be done is not liable as an employer under this division.