California Code, Government Code - GOV § 22201.7

The board shall upon the request of the legislative or governing body of any public agency, other than a school district, made after affirmative, secret vote of a majority of the eligible employees of the public agency in the class to be excluded, execute a modification to the agreement in conformity with federal law and regulations to exclude from coverage in any coverage group of such agency service in any class or classes of part-time positions.