CA Gov't Code Section 37101.7

(a)

In accordance with the provisions of subdivision (b), the legislative body may license for revenue, and fix the license tax upon, persons who transact in the city the business of a contractor licensed pursuant to Chapter 9 (commencing with Section 7000) of Division 3 of the Business and Professions Code.

(b)

The ordinance which adopts the license and license tax shall not impose a greater license tax upon those persons subject to it who, as contractors, have no fixed place of business within the city, than upon those contractors who have a fixed place of business within the city; provided, however, that such ordinance may impose a license tax graduated according to gross receipts attributable to contracting work done within a city, regardless of whether or not the contractor has a fixed place of business within the city.