Cal. Civ. Code § 226-B

  § 226-b. Right to sublease or assign. 1. Unless a greater right to
assign is conferred by the lease, a tenant renting a residence may not
assign his lease without the written consent of the owner, which consent
may be unconditionally withheld without cause provided that the owner
shall release the tenant from the lease upon request of the tenant upon
thirty days notice if the owner unreasonably withholds consent which
release shall be the sole remedy of the tenant. If the owner reasonably
withholds consent, there shall be no assignment and the tenant shall not
be released from the lease.
  2. (a) A tenant renting a residence pursuant to an existing lease in a
dwelling having four or more residential units shall have the right to
sublease his premises subject to the written consent of the landlord in
advance of the subletting. Such consent shall not be unreasonably
withheld.
  (b) The tenant shall inform the landlord of his intent to sublease by
mailing a notice of such intent by certified mail, return receipt
requested. Such request shall be accompanied by the following
information: (i) the term of the sublease, (ii) the name of the proposed
sublessee, (iii) the business and permanent home address of the proposed
sublessee, (iv) the tenant's reason for subletting, (v) the tenant's
address for the term of the sublease, (vi) the written consent of any
cotenant or guarantor of the lease, and (vii) a copy of the proposed
sublease, to which a copy of the tenant's lease shall be attached if
available, acknowledged by the tenant and proposed subtenant as being a
true copy of such sublease.
  (c) Within ten days after the mailing of such request, the landlord
may ask the tenant for additional information as will enable the
landlord to determine if rejection of such request shall be
unreasonable. Any such request for additional information shall not be
unduly burdensome.  Within thirty days after the mailing of the request
for consent, or of the additional information reasonably asked for by
the landlord, whichever is later, the landlord shall send a notice to
the tenant of his consent or, if he does not consent, his reasons
therefor. Landlord's failure to send such a notice shall be deemed to be
a consent to the proposed subletting. If the landlord consents, the
premises may be sublet in accordance with the request, but the tenant
thereunder, shall nevertheless remain liable for the performance of
tenant's obligations under said lease. If the landlord reasonably
withholds consent, there shall be no subletting and the tenant shall not
be released from the lease. If the landlord unreasonably withholds
consent, the tenant may sublet in accordance with the request and may
recover the costs of the proceeding and attorneys fees if it is found
that the owner acted in bad faith by withholding consent.
  3. The provisions of this section shall apply to leases entered into
or renewed before or after the effective date of this section, however
they shall not apply to public housing and other units for which there
are constitutional or statutory criteria covering admission thereto nor
to a proprietary lease, viz.: a lease to, or held by, a tenant entitled
thereto by reason of ownership of stock in a corporate owner of premises
which operates the same on a cooperative basis.
  4. With respect to units covered by the emergency tenant protection
act of nineteen seventy-four or the rent stabilization law of nineteen
hundred sixty-nine the exercise of the rights granted by this section
shall be subject to the applicable provisions of such laws. Nothing
contained in this section two hundred twenty-six-b shall be deemed to
affect the rights, if any, of any tenant subject to title Y of chapter
51 of the administrative code of the city of New York or the emergency
housing rent control law.
  5. Any sublet or assignment which does not comply with the provisions
of this section shall constitute a substantial breach of lease or
tenancy.
  6. Any provision of a lease or rental agreement purporting to waive a
provision of this section is null and void.
  7. The provisions of this section except for items in paragraph (b) of
subdivision two of this section not previously required, shall apply to
all actions and proceedings pending on the effective date of this
section.
  8. Nothing contained in this section shall be deemed to prevent or
limit the right of a tenant to sell improvements to a unit pursuant to
article seven-C of the multiple dwelling law.