Cal. Pen. Code § 2934
Under rules prescribed by the Secretary of the Department of Corrections and Rehabilitation, a prisoner subject to the provisions of Section 2931 may waive the right to receive time credits as provided in Section 2931 and be subject to the provisions of Section 2933. In order to exercise a waiver under this section, a prisoner must apply in writing to the Department of Corrections. A prisoner exercising a waiver under this section shall retain only that portion of good behavior and participation credits, which have not been forfeited pursuant to Section 2932, attributable to the portion of the sentence served by the prisoner prior to the effective date of the waiver. A waiver under this section shall, if accepted by the department, become effective at a time to be determined by the Secretary of the Department of Corrections and Rehabilitation.
Ca. Pen. Code § 2934