California Code, Health and Safety Code - HSC § 119080

(a) Every manufacturer of a portable or permanent electrical generator that is capable of being connected either permanently or temporarily to a commercial, industrial, or residential structure's electrical system, shall include a warning statement in the generator's instruction manual and a legible warning label on the generator that states the requirement of Section 119075 and explains the electrical hazards of backfeed into a utility's distribution system.  The same warning information shall be included in all advertisements offering portable electric generators.

(b) No person or public agency shall sell, rent to another person or public agency, or offer for sale or rent to another person or public agency a portable electrical generator unless the legible warning label is on a visible surface of the generator.