Cal. Civ. Code § 223-B

  § 223-b. Retaliation by landlord against tenant. 1. No landlord of
premises or units to which this section is applicable shall serve a
notice to quit upon any tenant or commence any action to recover real
property or summary proceeding to recover possession of real property in
retaliation for:
  a. A good faith complaint, by or in behalf of the tenant, to the
landlord, the landlord's agent or a governmental authority of the
landlord's alleged violation of any health or safety law, regulation,
code, or ordinance, the warranty of habitability under section two
hundred thirty-five-b of this article, the duty to repair under sections
seventy-eight, seventy-nine, and eighty of the multiple dwelling law or
section one hundred seventy-four of the multiple residence law, or any
law or regulation which has as its objective the regulation of premises
used for dwelling purposes or which pertains to the offense of rent
gouging in the third, second or first degree; or
  b. Actions taken in good faith, by or in behalf of the tenant, to
secure or enforce any rights under the lease or rental agreement, the
warranty of habitability under section two hundred thirty-five-b of this
article, the duty to repair under sections seventy-eight, seventy-nine,
and eighty of the multiple dwelling law or section one hundred
seventy-four of the multiple residence law, or under any other law of
the state of New York, or of its governmental subdivisions, or of the
United States which has as its objective the regulation of premises used
for dwelling purposes or which pertains to the offense of rent gouging
in the third, second or first degree; or
  c. The tenant's participation in the activities of a tenant's
organization.
  2. No landlord of premises or units to which this section is
applicable or such landlord's agent shall substantially alter the terms
of the tenancy in retaliation for any actions set forth in paragraphs a,
b, and c of subdivision one of this section. Substantial alteration
shall include, but is not limited to, the refusal to continue a tenancy
of the tenant, upon expiration of the tenant's lease, to renew the lease
or offer a new lease, or offering a new lease with an unreasonable rent
increase; provided, however, that a landlord shall not be required under
this section to offer a new lease or a lease renewal for a term greater
than one year.
  3. A landlord shall be subject to a civil action for damages,
attorney's fees and costs and other appropriate relief, including
injunctive and other equitable remedies, as may be determined by a court
of competent jurisdiction in any case in which the landlord has violated
the provisions of this section.
  4. In any action to recover real property or summary proceeding to
recover possession of real property, judgment shall be entered for the
tenant if the court finds that the landlord is acting in retaliation for
any action set forth in paragraphs a, b, and c of subdivision one of
this section. Retaliation shall be asserted as an affirmative defense in
such action or proceeding. The tenant shall not be relieved of the
obligation to pay any rent for which he is otherwise liable.
  5. In an action or proceeding instituted against a tenant of premises
or a unit to which this section is applicable, a rebuttable presumption
that the landlord is acting in retaliation shall be created if the
tenant establishes that the landlord served a notice to quit, or
instituted an action or proceeding to recover possession, or attempted
to substantially alter the terms of the tenancy, within one year after:
  a. A good faith complaint was made, by or in behalf of the tenant, to
the landlord, the landlord's agent or a governmental authority of the
landlord's violation of any health or safety law, regulation, code, or
ordinance, the warranty of habitability under section two hundred
thirty-five-b of this article, the duty to repair under sections
seventy-eight, seventy-nine, and eighty of the multiple dwelling law or
section one hundred seventy-four of the multiple residence law, or any
law or regulation which has as its objective the regulation of premises
used for dwelling purposes or which pertains to the offense of rent
gouging in the third, second or first degree; or
  b. The tenant in good faith took action to secure or enforce against
the landlord or his agents any rights under the lease or rental
agreement, the warranty of habitability under section two hundred
thirty-five-b of this article, the duty to repair under sections
seventy-eight, seventy-nine, and eighty of the multiple dwelling law or
section one hundred seventy-four of the multiple residence law, or under
any other law of the state of New York, or of its governmental
subdivisions, or of the United States which has as its objective the
regulation of premises used for dwelling purposes or which pertains to
the offense of rent gouging in the third, second or first degree.
  c. Judgment under subdivision three or four of this section was
entered for the tenant in a previous action between the parties; or an
inspection was made, an order was entered, or other action was taken as
a result of a complaint or act described in paragraph a or b of this
subdivision.
  The effect of the presumption shall be to require the landlord to
establish a non-retaliatory motive for his acts by a preponderance of
the evidence.
  5-a. Any lease provision which seeks to assess a fee, penalty or
dollar charge, in addition to the stated rent, against a tenant because
such tenant files a bona fide complaint with the landlord, the
landlord's agent or a building code officer regarding the condition of
such tenant's leased premises shall be null and void as being against
public policy. A landlord or agent of the landlord who seeks to enforce
such a fee, penalty or charge shall be liable to the tenant for triple
the amount of such fee, penalty or charge.
  6. This section shall apply to all rental residential premises except
owner-occupied dwellings with less than four units. However, its
provisions shall not be given effect in any case in which it is
established that the condition from which the complaint or action arose
was caused by the tenant, a member of the tenant's household, or a guest
of the tenant. Nor shall it apply in a case where a tenancy was
terminated pursuant to the terms of a lease as a result of a bona fide
transfer of ownership.