Legal Question in Employment Law in California

Yup. It is up to the employer whether they pay for certification maintenance or not. It's a benefit, not a right. When I have been an employee attorney, some firms have paid for my mandatory continuing legal education classes, some have given me a "professional development" expense account to use for classes, or books, or client development, or whatever, and others have paid for nothing beyond my salary. All three options are perfectly legal.

Your employer is well within its rights to require you to renew your certification without any financial assistance. It is your obligation to satisfy the requirements of your job.