Cal. Gov. Code § 56737

When a change of organization or a reorganization includes the annexation of inhabited territory to a city and the assessed value of land within the territory equals one-half or more of the assessed value of land within the city, or the number of registered voters residing within the territory equals one-half or more of the number of registered voters residing within the city, the commission may determine as a condition of the proposal that the change of organization or reorganization shall also be subject to confirmation by the voters in an election to be called, held, and conducted within the territory of the city to which annexation is proposed.