California Code, Labor Code - LAB § 513

If an employer approves a written request of an employee to make up work time that is or would be lost as a result of a personal obligation of the employee, the hours of that makeup work time, if performed in the same workweek in which the work time was lost, may not be counted towards computing the total number of hours worked in a day for purposes of the overtime requirements specified in Section 510 or 511, except for hours in excess of 11 hours of work in one day or 40 hours in one workweek.  An employee shall provide a signed written request for each occasion that the employee makes a request to make up work time pursuant to this section.  An employer is prohibited from encouraging or otherwise soliciting an employee to request the employer's approval to take personal time off and make up the work hours within the same week pursuant to this section.