Cal. CIV § 1997.250

A restriction on use of leased property by a tenant may require the landlord’s consent for a change in use subject to any express standard or condition for giving or withholding consent, including, but not limited to, either of the following: (a) The landlord’s consent may not be unreasonably withheld. (b) The landlord’s consent may be withheld subject to express standards or conditions.